Updated on 2024/05/01

写真a

 
HIGASHIWAKI MASATAKA
 
Organization
Graduate School of Engineering Division of Physics and Electronics Professor
School of Engineering Department of Physics and Electronics
Title
Professor
Affiliation
Institute of Engineering
Contact information
メールアドレス
Affiliation campus
Nakamozu Campus

Position

  • Graduate School of Engineering Division of Physics and Electronics 

    Professor  2022.04 - Now

  • School of Engineering Department of Physics and Electronics 

    Professor  2022.04 - Now

Degree

  • 工学博士 ( Osaka University )

Research Areas

  • Manufacturing Technology (Mechanical Engineering, Electrical and Electronic Engineering, Chemical Engineering) / Electric and electronic materials

  • Nanotechnology/Materials / Nanomaterials

  • Nanotechnology/Materials / Nano/micro-systems

  • Manufacturing Technology (Mechanical Engineering, Electrical and Electronic Engineering, Chemical Engineering) / Electron device and electronic equipment

Research Interests

  • transistor

  • Gallium oxide

  • Molecular beam epitaxy (MBE)

  • Gallium nitride

Professional Memberships

  • THE JAPAN SOCIETY OF APPLIED PHYSICS

    1994.08 - Now

  • THE INSTITUTE OF ELECTRONICS, INFORMATION AND COMMUNICATION ENGINEERS.

    2011.11 - Now

  • IEEE

    2007 - Now

Committee Memberships (off-campus)

  • 企画主査   一般社団法人ワイドギャップ半導体学会  

    2021.04 - Now 

  • 幹事   応用物理学会 先進パワー半導体分科会  

    2020.04 - Now 

  • APEX/JJAP編集委員   公益社団法人応用物理学会  

    2020.04 - 2023.03 

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    Web システムを利用した論文審査処理と会議出席

  • 委員   電気学会「次世代化合物電子デバイスとその応用調査専門委員会」  

    2013.04 - Now 

  • Vice Chair   IEEE東京セクション Chapter Promotion Committee  

    2013.04 - 2015.03 

  • 委員   応用物理学会 論文賞委員会  

    2013.04 - 2015.03 

  • 専門委員   電子情報通信学会 電子デバイス(ED)研究専門委員会  

    2011.06 - Now 

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    専門委員(2019年度-現在)
    幹事(2017-2018年度)
    幹事補佐(2015-2016年度)
    専門委員(2011-2014年度)

  • 企画委員   日本学術振興会「ワイドギャップ半導体光・電子デバイス」第162委員会  

    2006.04 - 2021.03 

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    企画委員(2013-2020年度)
    委員(2006-2012年度)

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Awards

  • 2023 Highly Cited Researcher

    Masataka Higashiwaki

    2023.11   Clarivate Analytics  

  • IEEE Fellow

    Masataka Higashiwaki

    2023.01   Institute of Electrical and Electronics Engineers (IEEE)   for contributions to gallium oxide electronics and millimeter-wave gallium nitride transistors

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    Country:United States

  • The 54th Ichimura Prize in Science for Distinguished Achievement

    Masataka Higashiwaki

    2022.04   Ichimura Foundation for New Technology   Pioneering research and development on gallium oxide devices

  • 2021 Highly Cited Researcher

    Masataka Higashiwaki

    2021.11   Clarivate Analytics  

  • Nakamura Lecturer Award

    Masataka HIGASHIWAKI

    2018.02   University of California, Santa Barbara  

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    Country:United States

  • The JSPS Award

    Masataka HIGASHIWAKI

    2015.02   Japan Society of the Promotion of Science  

  • The 27th Fuji-Sankei Business i Advanced Technology Award

    Masataka Higashiwaki, Kohei Sasaki, Akito Kuramata, Shigenobu Yamakoshi

    2013.07   Research and development of gallium oxide power devices

  • The Research Encouragement Award

    Masataka Higashiwaki

    2009.03   Marubun Research Promotion Foundation   Research and development of ultra-high-frequency gallium nitride transistors

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    Country:Japan

  • The Young Scientist Award

    Masataka Higashiwaki

    2007.10   The International Symposium on Compound Semiconductors (ISCS)   For contributions to the development of GaN-based millimeter-wage high electron mobility Transistors

  • 第28回応用物理学会論文賞(JJAP論文賞)

    2006.08   応用物理学会  

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    Country:Japan

  • 第27回応用物理学会論文賞(JJAP論文奨励賞)

    2005.09   応用物理学会  

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    Country:Japan

  • 第16回応用物理学会講演奨励賞

    2004.09   応用物理学会  

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    Country:Japan

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Job Career (off-campus)

  • Osaka Metropolitan University   Department of Physics and Electronics

    2022.04 - Now

  • National Institute of Information and Communications Technology   Green ICT Device Laboratory, Koganei Frontier Research Center, Advanced ICT Research Institute   Director

    2021.04 - Now

  • University of Bristol   The Center for Device Thermography and Reliability (CDTR)   Honorary Professor(兼務)

    2021.05 - Now

  • National Institute of Information and Communications Technology   Green ICT Device Laboratory, Koganei Frontier Research Center, Advanced ICT Research Institute   Director

    2021.04 - 2022.03

  • Hokkaido University   Research Center for Integrated Quantum Electronics

    2017.04 - 2018.03

  • National Institute of Information and Communications Technology   Green ICT Device Advanced Development Center, Advanced ICT Research Institute   Director

    2016.04 - 2021.03

  • (株)ノベルクリスタルテクノロジー   顧問(兼務)

    2016.03 - Now

  • National Institute of Information and Communications Technology   Advanced ICT Research Institute, Green ICT Device Advanced Development Center   Director

    2013.12 - 2016.03

  • National Institute of Information and Communications Technology   Advanced ICT Research Institute   Chief Senior Researcher

    2012.10 - 2013.11

  • Kogakuin University

    2011.04 - 2017.03

  • Osaka University   Graduate School of Engineering Science

    2011.04 - 2012.03

  • JST PRESTO   Researcher

    2010.04 - 2013.03

  • National Institute of Information and Communications Technology   Senior Researcher

    2010.04 - 2012.09

  • University of California, Santa Barbara   Department of Electrical and Computer Engineering,   Project Scientist

    2007.09 - 2010.03

  • National Institute of Information and Communications Technology   Senior Researcher

    2004.10 - 2007.08

  • CRL (currently, NICT)

    2000.04 - 2004.09

  • Japan Society for the Promotion of Science   Postdoctral Fellow

    1998.04 - 2000.03

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Education

  • Osaka University   The second semester of doctoral program   Graduated/Completed

    1996.04 - 1998.03

  • Osaka University   The first semester of doctoral program   Graduated/Completed

    1994.04 - 1996.03

  • Osaka University   Bachelor's Course   Graduated/Completed

    1990.04 - 1994.03

Papers

  • Extraction of Sub-Threshold Mobility in Ga2O3 Lateral Transistors From AC Conductance Reviewed International coauthorship

    Abhishek Mishra, Michael J. Uren, Matthew D. Smith, Zequan Chen, Aditya K. Bhat, Masataka Higashiwaki, and Martin Kuball

    IEEE Electron Device Letters   44 ( 12 )   1943 - 1946   2023.11

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    Publishing type:Research paper (scientific journal)   International / domestic magazine:International journal  

    DOI: 10.1109/LED.2023.3325373

  • Suppression of drain current leakage and short-channel effect in lateral Ga2O3 RF MOSFETs using (AlxGa1−x)2O3 back-barrier Reviewed

    Takumi Ohtsuki, Takafumi Kamimura, and Masataka Higashiwaki

    IEEE Electron Device Letters   44 ( 11 )   1829 - 1832   2023.10

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    Authorship:Last author   Publishing type:Research paper (scientific journal)   International / domestic magazine:International journal  

    DOI: 10.1109/LED.2023.3318215

  • Crystallinity degradation and defect development in (AlxGa1−x)2O3 thin films with increased Al composition Reviewed

    Takumi Ohtsuki and Masataka Higashiwaki

    Journal of Vacuum Science & Technology A   41 ( 4 )   042712-1 - 042712-6   2023.06

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    Authorship:Last author   Publishing type:Research paper (scientific journal)   International / domestic magazine:International journal  

    DOI: 10.1116/6.0002625

  • Thermodynamic analysis of molecular beam epitaxy of group-III sesquioxides Reviewed

    Rie Togashi, Ken Goto, Masataka Higashiwaki, and Yoshinao Kumagai

    Japanese Journal of Applied Physics   62 ( 5 )   055503-1 - 055503-8   2023.05

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    Publishing type:Research paper (scientific journal)   International / domestic magazine:International journal  

    DOI: 10.35848/1347-4065/accfd8

  • Electrical properties and energy band alignments of p-Si/n-Ga2O3 and p+-Si/n-Ga2O3 heterostructures fabricated by surface-activated bonding Reviewed

    Zhenwei Wang, Takahiro Kitada, Daiki Takatsuki, Jianbo Liang, Naoteru Shigekawa, and Masataka Higashiwaki

    Journal of Applied Physics   133 ( 19 )   194503-1 - 194503-7   2023.05

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    Authorship:Last author   Publishing type:Research paper (scientific journal)   International / domestic magazine:International journal  

    DOI: 10.1063/5.0128554

  • Modelling of impedance dispersion in lateral β-Ga2O3 MOSFETs due to parallel conductive Si-accumulation layer Reviewed International coauthorship

    Zequan Chen, Abhishek Mishra, Aditya K. Bhat, Matthew D. Smith, Michael J. Uren, Sandeep Kumar, Masataka Higashiwaki, and Martin Kuball

    Applied Physics Express   16 ( 4 )   044002-1 - 044002-4   2023.04

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    Publishing type:Research paper (scientific journal)   International / domestic magazine:International journal  

    DOI: 10.35848/1882-0786/accc09

  • β-Ga2O3 material properties, growth technologies, and devices: a review Invited Reviewed

    Masataka Higashiwaki

    AAPPS Bulletin   32   3-1 - 3-14   2022.12

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    Authorship:Lead author, Last author, Corresponding author   Publishing type:Research paper (scientific journal)   International / domestic magazine:International journal  

    DOI: 10.1007/s43673-021-00033-0

    Repository URL: http://hdl.handle.net/10466/0002000229

  • Thermodynamic analysis of β-Ga2O3 growth by molecular beam epitaxy Reviewed

    Rie Togashi, Haruka Ishida, Ken Goto, Masataka Higashiwaki, Yoshinao Kumagai

    Japanese Journal of Applied Physics   62 ( 1 )   015501-1 - 015501-6   2022.10( ISSN:0021-4922

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    Publishing type:Research paper (scientific journal)   International / domestic magazine:International journal  

    Abstract

    Thermodynamic analyses of β-Ga<sub>2</sub>O<sub>3</sub> growth by both ozone and plasma-assisted molecular beam epitaxy were performed. In either case, the growth mechanism was found to differ depending on whether the input VI/III ratio was above or below 1.5. Under O-rich conditions (VI/III &gt; 1.5), the driving force for β-Ga<sub>2</sub>O<sub>3</sub> growth (ΔP<sub>Ga<sub>2</sub>O<sub>3</sub></sub>) was determined to increase linearly with increasing Ga input partial pressure (P°<sub>Ga</sub>) because almost all the supplied Ga was used for growth of the β-Ga<sub>2</sub>O<sub>3</sub>. In contrast, Ga-rich conditions (VI/III &lt; 1.5) caused ΔP<sub>Ga<sub>2</sub>O<sub>3</sub></sub> to decrease. Etching of the β-Ga<sub>2</sub>O<sub>3</sub> occurred with increasing P°<sub>Ga</sub> due to the formation of volatile Ga<sub>2</sub>O. This work also demonstrated that the use of ozone allowed growth at higher temperatures than the use of O radicals. The calculated results were in good agreement with experimental values, indicating that β-Ga<sub>2</sub>O<sub>3</sub> growth by molecular beam epitaxy can be explained by thermodynamics.

    DOI: 10.35848/1347-4065/ac9bb2

    Other URL: https://iopscience.iop.org/article/10.35848/1347-4065/ac9bb2/pdf

    Repository URL: http://hdl.handle.net/10466/0002000238

  • Wide bandgap semiconductor materials and devices Invited Reviewed International coauthorship

    Joel B. Varley, Bo Shen, Masataka Higashiwaki

    Journal of Applied Physics   131 ( 23 )   230401-1 - 230401-4   2022.06

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    Authorship:Last author   Publishing type:Research paper (scientific journal)   International / domestic magazine:International journal  

    DOI: 10.1063/5.0100601

    Repository URL: http://hdl.handle.net/10466/0002000230

  • Fabrication of β-Ga2O3/Si heterointerface and characterization of interfacial structures for high-power device applications Reviewed

    Jianbo Liang, Daiki Takatsuki, Masataka Higashiwaki, Yasuo Shimizu, Yutaka Ohno, Yasuyoshi Nagai, Naoteru Shigekawa

    JAPANESE JOURNAL OF APPLIED PHYSICS   61 ( SF )   SF1001-1 - SF1001-7   2022.06( ISSN:0021-4922

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    Publishing type:Research paper (scientific journal)   International / domestic magazine:International journal  

    In this work, we fabricated Ga2O3(001)/Si(100) and Ga2O3(010)/Si(100) heterointerfaces by surface activated bonding at room temperature and investigated the effect of Si thickness on the thermal stability of the heterointerfaces by heating the bonding samples at different temperatures. The heterointerface with a thin Si exhibited a good thermal stability at 1000 degrees C. A 4 nm thick intermediate layer with a uniform thickness was formed at the as-bonded Ga2O3(001)/Si(100) heterointerface, but for the as-bonded Ga2O3(010)/Si(100) heterointerface, an intermediate layer with a non-uniform thickness was formed. The thickness of both intermediate layers ranged from 3.6 to 5.4 nm and decreased after annealing at 500 degrees C, followed by an increase after annealing at 1000 degrees C. The component of the intermediate layer includes Ga, O, and Si atoms.

    DOI: 10.35848/1347-4065/ac4c6c

    Repository URL: http://hdl.handle.net/10466/0002000234

  • Vertical β-Ga2O3 Schottky barrier diodes with trench staircase field plate Reviewed

    Sandeep Kumar, Hisashi Murakami, Yoshinao Kumagai, Masataka Higashiwaki

    APPLIED PHYSICS EXPRESS   15 ( 5 )   054001-1 - 054001-3   2022.05( ISSN:1882-0778

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    This study presents vertical Ga2O3 Schottky barrier diodes (SBDs) with a staircase field plate on a deep trench filled with SiO2. It was clarified from device simulation that at high reverse voltage operation, the staircase field plate and the deep trench can effectively alleviate electric field concentration in the Ga2O3 drift layer and the SiO2 layer, respectively. The Ga2O3 SBDs successfully demonstrated superior device characteristics typified by an on-resistance of 7.6 m omega cm(2) and an off-state breakdown voltage of 1.66 kV. These results offer the availability of the trench staircase field plate as an edge termination structure for the development of Ga2O3 SBDs.

    DOI: 10.35848/1882-0786/ac620b

    Repository URL: http://hdl.handle.net/10466/0002000236

  • Effect of substrate orientation on homoepitaxial growth of β-Ga2O3 by halide vapor phase epitaxy Reviewed

    Ken Goto, Hisashi Murakami, Akito Kuramata, Shigenobu Yamakoshi, Masataka Higashiwaki, Yoshinao Kumagai

    APPLIED PHYSICS LETTERS   120 ( 10 )   102102-1 - 102102-6   2022.03( ISSN:0003-6951

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    The influence of substrate orientation on homoepitaxial growth of beta-gallium oxide by halide vapor phase epitaxy was investigated. Substrates were cut at various angles & UDelta;(b) from the (001) plane (& UDelta;(b) = 0 & DEG;) to the (010) plane (& UDelta;(b) = 90 & DEG;) of bulk crystals grown by the edge-defined film-fed growth method. The growth rate increased with increasing absolute value of & UDelta;(b) near the (001). However, from the (001) to the (010), as & UDelta;(b) increased, the growth rate decreased sharply, and streaky grooves observed in the grown layer on the (001) substrate became triangular pits. The length of the pits decreased with increasing & UDelta;(b), and a pit-free homoepitaxial layer grew at & UDelta;(b) & AP; 60 & DEG;. The valley line of the pits was parallel to the [010] direction; therefore, the length of the pits decreased with increasing & UDelta;(b). In addition, transmission electron microscopy observations of the deepest part of a pit revealed that the pits originate from dislocations propagating in the substrate at an angle of 60 & DEG; with respect to the (001) plane. Therefore, pits are not formed on the grown layer surface when the & UDelta;(b) of the substrate is & SIM;60 & DEG;, because its surface is substantially parallel to the dislocations. The homoepitaxial growth of a pit-free layer on the (011) substrate (& UDelta;(b) = 61.7 & DEG;) was demonstrated, and void defects and dislocations in the substrate were confirmed by the etch-pit method to not be inherited by the homoepitaxial layer.

    DOI: 10.1063/5.0087609

    Repository URL: http://hdl.handle.net/10466/0002000233

  • Fabrication of n-Si/n-Ga2O3 heterojunctions by surface-activated bonding and their electrical properties Reviewed

    Zhenwei Wang, Daiki Takatsuki, Jianbo Liang, Takahiro Kitada, Naoteru Shigekawa, Masataka Higashiwaki

    JOURNAL OF APPLIED PHYSICS   131 ( 7 )   074501-1 - 074501-9   2022.02( ISSN:0021-8979

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    We studied electrical properties of n-Si/n-Ga2O3 heterojunctions fabricated by surface-activated bonding. The energy barrier heights (q phi(b)) at the Si/Ga2O3 interface for different reverse voltages (V-rev) were derived from temperature-dependent current density-voltage (J-V-T) characteristics. With shifting V-rev to the negative direction, q phi(b) gradually decreased and reached a constant value due to negatively charged interface states. The conduction band offset at the heterointerface was estimated to be 0.18 eV from the V-rev dependence of q phi(b). The q phi(b) calculated from a capacitance of the heterojunction at thermal equilibrium was larger than those derived from the J-V-T characteristics, attributing to spatially inhomogeneous q phi(b) caused by the non-uniform distribution of the charged interface states. The density of shallow interface states was also extracted from the reverse J-V-T characteristics, which was estimated to be about 6 x 10(12) cm(-2) eV(-1).

    DOI: 10.1063/5.0080734

    Repository URL: http://hdl.handle.net/10466/0002000235

  • β-Gallium oxide power electronics Invited Reviewed International coauthorship

    Andrew J. Green, James Speck, Grace Xing, Peter Moens, Fredrik Allerstam, Krister Gumaelius, Thomas Neyer, Andrea Arias-Purdue, Vivek Mehrotra, Akito Kuramata, Kohei Sasaki, Shinya Watanabe, Kimiyoshi Koshi, John Blevins, Oliver Bierwagen, Sriram Krishnamoorthy, Kevin Leedy, Aaron R. Arehart, Adam T. Neal, Shin Mou, Steven A. Ringel, Avinash Kumar, Ankit Sharma, Krishnendu Ghosh, Uttam Singisetti, Wenshen Li, Kelson Chabak, Kyle Liddy, Ahmad Islam, Siddharth Rajan, Samuel Graham, Sukwon Choi, Zhe Cheng, Masataka Higashiwaki

    APL MATERIALS   10 ( 2 )   029201-1 - 029201-40   2022.02( ISSN:2166-532X

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    Authorship:Last author   Publishing type:Research paper (scientific journal)   International / domestic magazine:International journal  

    Gallium Oxide has undergone rapid technological maturation over the last decade, pushing it to the forefront of ultra-wide band gap semiconductor technologies. Maximizing the potential for a new semiconductor system requires a concerted effort by the community to address technical barriers which limit performance. Due to the favorable intrinsic material properties of gallium oxide, namely, critical field strength, widely tunable conductivity, mobility, and melt-based bulk growth, the major targeted application space is power electronics where high performance is expected at low cost. This Roadmap presents the current state-of-the-art and future challenges in 15 different topics identified by a large number of people active within the gallium oxide research community. Addressing these challenges will enhance the state-of-the-art device performance and allow us to design efficient, high-power, commercially scalable microelectronic systems using the newest semiconductor platform. (c) 2022 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license(http://creativecommons.org/licenses/by/4.0/).

    DOI: 10.1063/5.0060327

    Repository URL: http://hdl.handle.net/10466/0002000232

  • A trapping tolerant drain current based temperature measurement of β-Ga2O3 MOSFETs Reviewed International coauthorship

    Xiang Zheng, Taylor Moule, James W. Pomeroy, Masataka Higashiwaki, Martin Kuball

    APPLIED PHYSICS LETTERS   120 ( 7 )   073502-1 - 073502-4   2022.02( ISSN:0003-6951

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    Publishing type:Research paper (scientific journal)   International / domestic magazine:International journal  

    The drain current temperature dependence is an efficient way to determine the channel temperature in semiconductor devices; however, it has been challenging to use due to the potential interference of trapping effects. A trapping tolerant method is proposed, illustrated here for Ga2O3 MOSFETs, making in situ temperature measurements possible, allowing a thermal resistance of 59 K.mm/W to be measured in Ga2O3 MOSFETs. However, neglecting the effect of trapping causes an error of similar to 15% in the channel temperature measured using the drain current. 3D simulations show that the measured channel temperature is the average temperature value between source and drain contact.

    DOI: 10.1063/5.0069655

    Repository URL: http://hdl.handle.net/10466/0002000231

  • Deep levels and conduction processes in nitrogen-implanted Ga2O3 Schottky barrier diodes International coauthorship

    C. De Santi, M. Fregolent, M. Buffolo, M. Higashiwaki, G. Meneghesso, E. Zanoni, M. Meneghini

    Proceedings of SPIE - The International Society for Optical Engineering   12002   1200209-1 - 1200209-6   2022( ISSN:0277786X ( ISBN:9781510648753

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    Publishing type:Research paper (international conference proceedings)   International / domestic magazine:International journal  

    DOI: 10.1117/12.2607613

    Repository URL: http://hdl.handle.net/10466/0002000237

  • Impact of thermal annealing on deep levels in nitrogen-implanted β-Ga2O3 Schottky barrier diodes Reviewed International coauthorship

    Manuel Fregolent, Carlo De Santi, Matteo Buffolo, Masataka Higashiwaki, Gaudenzio Meneghesso, Enrico Zanoni, Matteo Meneghini

    JOURNAL OF APPLIED PHYSICS   130 ( 24 )   2021.12( ISSN:0021-8979

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    Publishing type:Research paper (scientific journal)   International / domestic magazine:International journal  

    Understanding the properties of N-implanted beta-Ga2O3 is fundamental for the optimization of doping and isolation structures based on gallium oxide. This paper reports an extensive analysis of the impact of thermal annealing on the concentration and properties of deep levels in N-implanted beta-Ga2O3 Schottky barrier diodes by means of capacitance isothermal transient spectroscopy. Samples with annealing temperatures from 800 to 1200 & DEG;C were considered. The original results presented in this paper demonstrate the following: (a) The instability of current-voltage characteristics detected for all the samples under test can be attributed to the presence of three electron traps with activation energies of 0.6, 0.7, and 1 eV, consistent with previous reports in beta-Ga2O3. (b) The detected traps are not the nitrogen level but intrinsic defects whose concentration is increased by the implantation process. (c) The concentration of deep levels decreases as the annealing temperature increases, demonstrating that the annealing process can effectively restore the quality of the material while keeping the conductivity decrease related to the presence of the nitrogen. Finally, (d) we demonstrate that the residual leakage and the turn-on voltage shift are correlated with the Arrhenius signature of the detected deep levels. An interpretation is proposed to explain the measurement results.

    DOI: 10.1063/5.0065434

  • beta-Gallium Oxide Devices: Progress and Outlook

    Masataka Higashiwaki

    PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS   15 ( 11 )   2021.11( ISSN:1862-6254

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    Publishing type:Research paper (scientific journal)  

    Beta-gallium oxide (beta-Ga2O3) has a history of research and development for over 70 years; however, it has attracted little attention as a semiconductor material for a long time. The situation has drastically changed in the past decade, and research on its material properties and developments of growth and device technologies has become active worldwide, mainly from expectations for applications to next-generation power devices. Most of the specific material properties are attributed to its extremely large bandgap energy of 4.5 eV. The other important material feature is that large-size single-crystal bulks can be synthesized by melt growth methods. Herein, after introducing the material properties of beta-Ga2O3 that are important for electronic devices, the current status of bulk melt growth and epitaxial thin-film growth technologies is given. State-of-the-art beta-Ga2O3 diodes and transistors are also discussed, including future prospects.

    DOI: 10.1002/pssr.202100357

  • Fabrication of Ga2O3/Si direct bonding interface for high power device applications

    Jianbo Liang, Daiki Takatsuki, Yasuo Shimizu, Masataka Higashiwaki, Yutaka Ohno, Yasuyoshi Nagai, Naoteru Shigekawa

    2021 7th International Workshop on Low Temperature Bonding for 3D Integration (LTB-3D)   2021.10( ISBN:9781665405676

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    Publishing type:Research paper (international conference proceedings)   International / domestic magazine:International journal  

    DOI: 10.1109/LTB-3D53950.2021.9598435

  • Terahertz emission spectroscopy of GaN-based heterostructures

    Abdul Mannan, Kota Yamahara, Filchito Renee G. Bagsican, Kazunori Serita, Hironaru Murakami, Iwao Kawayama, Masataka Higashiwaki, Masayoshi Tonouchi

    Journal of Applied Physics   129 ( 24 )   245702 - 245702   2021.06( ISSN:0021-8979

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    Publishing type:Research paper (scientific journal)  

    This study investigates the band bending profile of gallium-nitride-based heterostructures with respect to the change in the direction of the induced current in the out-of-plane plane direction, which gives the phase of the terahertz emission peak and can be detected by laser THz emission microscopy. We use a wavelength-tunable laser THz emission spectroscope to observe the transport of charges within the band bending regions, excitation of nearby photocarriers, and carrier scattering. We observe flip-flop peak-to-peak THz emission waveforms for a GaN heterostructure field-effect transistor (FET) compared to a strong THz emission radiated from an Al0.3Ga0.7N/GaN high-electron-mobility-transistor (HEMT). The flip-flop THz emission indicates the emission from various interfaces inside the FET structure, and intense THz emission from the HEMT structure indicates band-edge excitation. Our results provide a valuable perspective for characterizing complex heterostructures that provide insight into possible defects, carrier mobilities, and band bending of multilayer interface electronic devices. Published under an exclusive license by AIP Publishing.

    DOI: 10.1063/5.0047402

  • Selective observation of transverse optical phonons of Au modes to evaluate free charge carrier parameters in β-Ga2O3 substrate and homoepitaxial film Reviewed

    Takeyoshi Onuma, Kohei Sasaki, Tomohiro Yamaguchi, Tohru Honda, Akito Kuramata, Shigenobu Yamakoshi, Masataka Higashiwaki

    APPLIED PHYSICS LETTERS   118 ( 25 )   2021.06( ISSN:0003-6951

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    Publishing type:Research paper (scientific journal)   International / domestic magazine:International journal  

    Polarized infrared reflectance spectra from beta-Ga2O3 (001) unintentionally doped (undoped) and Sn-doped substrates were investigated. Spectra from an undoped homoepitaxial film grown on the Sn-doped substrate were also investigated. By setting the electric field vector of the incident light E parallel to the crystallographic b-axis in the s-polarized configuration, the spectra for pure transverse optical phonons of A(u) modes were well reproduced by the Drude-Lorentz model. Subsequently, the free-carrier concentrations and carrier mobilities were determined to be in reasonable agreement with those determined by Hall-effect measurements, and at the same time, the film thickness was determined for the homoepitaxial layer. The results ensure the validity of the simplified optical model analyses for any arbitrary surface orientations where the b-axis is parallel to the surface only if no birefringence effects are present by choosing as E//b in s-polarized configuration.

    DOI: 10.1063/5.0059070

  • Ultrawide bandgap semiconductors

    Masataka Higashiwaki, Robert Kaplar, Julien Pernot, Hongping Zhao

    APPLIED PHYSICS LETTERS   118 ( 20 )   200401 - 200401   2021.05( ISSN:0003-6951

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    DOI: 10.1063/5.0055292

  • Effect of (AlGa)2O3 back barrier on device characteristics of β-Ga2O3 metal-oxide-semiconductor field-effect transistors with Si-implanted channel Reviewed

    Takafumi Kamimura, Yoshiaki Nakata, Masataka Higashiwaki

    JAPANESE JOURNAL OF APPLIED PHYSICS   60 ( 3 )   030906 - 030906   2021.03( ISSN:0021-4922

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    Publishing type:Research paper (scientific journal)   International / domestic magazine:International journal  

    An (AlGa)(2)O-3 back barrier was employed for Ga2O3 metal-oxide-semiconductor field-effect transistors (MOSFETs) with a Si-implanted n-Ga2O3 channel layer. The insertion of the back barrier led to strong confinement of electrons in the channel layer, and a shallower pinch-off characteristic with shifting a threshold gate voltage by +8 V was attained for the MOSFET with the back barrier compared to the conventional one without it. The excellent gate controllability represented by a subthreshold slope of 129 mV/decade was also achieved for the back-barrier MOSFET; whereas it was 337 mV/decade for the non-back-barrier one.

    DOI: 10.35848/1347-4065/abe3a4

  • Effect of thermal annealing on photoexcited carriers in nitrogen-ion-implanted beta-Ga2O3 crystals detected by photocurrent measurement Reviewed

    Masahiko Nakanishi, Man Hoi Wong, Tomohiro Yamaguchi, Tohru Honda, Masataka Higashiwaki, Takeyoshi Onuma

    AIP ADVANCES   11 ( 3 )   035237-1 - 035237-5   2021.03

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    Acceptor impurity doping is recognized as a functional tool to extend the capabilities and applications of beta -Ga2O3. The effect of thermal annealing on photoexcited carriers was characterized by measuring the photocurrent spectra of nitrogen (N)-ion-implanted beta -Ga2O3 crystals, where the N was found to cause less crystal damage to the crystal and much lower thermal diffusivity than Mg. The photocurrent intensity at 4.5-5.5 eV showed an increase with an increase in external bias, and the increase was attributed to the photo-generated non-equilibrium electrons and holes. The spectra under a positive external bias showed a distinct onset at 3.0-3.5 eV owing to optical transitions involving deep donor levels formed by the N-implantation. Spectrally integrated responsivity showed a significant change with the annealing temperature by reflecting the recovery of crystallinity and the thermal activation of N impurities. The results also indicate the formation of additional nonradiative recombination centers due to N-implantation.

    DOI: 10.1063/5.0031937

  • Aperture-limited conduction and its possible mechanism in ion-implanted current aperture vertical β-Ga2O3 MOSFETs Reviewed International coauthorship

    Man Hoi Wong, Hisashi Murakami, Yoshinao Kumagai, Masataka Higashiwaki

    Applied Physics Letters   118 ( 1 )   012102-1 - 012102-6   2021.01( ISSN:0003-6951

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    An anomalous diode-like turn-on behavior was observed in the drain characteristics of current aperture vertical beta -Ga2O3 transistors. This phenomenon was attributable to an electron barrier created by negative fixed charges in the aperture opening, through which electrons were funneled from the gated channel to the drift layer. Electrostatic analysis for deriving the turn-on voltage yielded effective sheet charge densities on the order of 10(11)-10(12)cm(-2). The charged species was conjectured to be acceptor-like point defects diffusing from nitrogen-implanted current blocking layers with an activation energy consistent with migration of gallium vacancies. These results alluded to a possible role of point-defect diffusion in the performance and reliability of ion-implanted Ga2O3 devices.

    DOI: 10.1063/5.0031561

  • Fundamental technologies for gallium oxide transistors

    Masataka Higashiwaki

    ULTRAWIDE BANDGAP SEMICONDUCTORS   107   1 - 22   2021( ISSN:0080-8784 ( ISBN:9780128228708

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    DOI: 10.1016/bs.semsem.2021.04.001

  • Carrier capture kinetics, deep levels, and isolation properties of β -Ga<sub>2</sub>O<sub>3</sub>Schottky-barrier diodes damaged by nitrogen implantation

    De Santi, C., Fregolent, M., Buffolo, M., Wong, M.H., Higashiwaki, M., Meneghesso, G., Zanoni, E., Meneghini, M.

    Applied Physics Letters   117 ( 26 )   2020.12( ISSN:00036951

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    DOI: 10.1063/5.0029295

  • Characterization of trap states in buried nitrogen-implanted β-Ga2O3

    Abhishek Mishra, Taylor Moule, Michael J Uren, Man Hoi Wong, Ken Goto, Hisashi Murakami, Yoshinao Kumagai, Masataka Higashiwaki, Martin Kuball

    Applied Physics Letters   117 ( 24 )   243505 - 243505   2020.12( ISSN:0003-6951

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    The advent of acceptor-type doping of beta -Ga2O3 through ion-implantation of nitrogen has opened a new design space for junction-type devices with estimated breakdown voltages in excess of a few kVs. However, the presence of deep states due to intrinsic defects in beta -Ga2O3 and implantation damage could be detrimental to the performance and reliability of such devices. We give a phenomenological description and experimental demonstration of the effects of nitrogen implantation in a buried blocking layer on the performance of transistors. The partial activation of acceptor-like states in the buried implanted region has been revealed and estimated to be similar to 20% through a junction spectroscopic technique involving substrate-bias and sub-bandgap illumination, which remains elusive to standard characterization techniques. The characterization technique, along with a space-charge model of the channel and band model of the buried implanted layer, has revealed the presence of photosensitive mid-bandgap (similar to 2.47eV below the conduction band) and tail states near the valence band edge of nitrogen-implanted beta -Ga2O3.

    DOI: 10.1063/5.0031480

  • Delay-time analysis in radio-frequency <bold>beta</bold>-Ga2O3 field effect transistors

    Takafumi Kamimura, Yoshiaki Nakata, Masataka Higashiwaki

    APPLIED PHYSICS LETTERS   117 ( 25 )   2020.12( ISSN:0003-6951

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    beta -Ga2O3 metal-oxide-semiconductor field-effect transistors (MOSFETs) with gate lengths (L-g) of 50-1000nm were fabricated, employing a thin channel layer formed by a shallow Si-ion implantation doping to maintain a high aspect ratio between an L-g and a gate-to-channel distance. The MOSFETs with L-g=200nm had a maximum drain current density of about 250mA/mm and a peak extrinsic transconductance of 17 mS/mm. The short-channel effect was well suppressed for the devices with L-g >= 200nm, leading to excellent RF device characteristics represented by a record maximum oscillation frequency of 27GHz at L-g=200nm. From simple delay-time analysis on the MOSFETs, the effective electron velocity passing through a region under the gate was estimated to be about 2x10(6)cm/s. Moreover, it was analyzed that the parasitic channel charging delay occupied a substantial proportion of the total delay due to a large sheet resistance of the Ga2O3 channel and thus limited their high-frequency device performance. These results suggest that both suppressing the short channel effect with a reduction in L-g to the sub-0.1-mu m range and minimizing the access resistance are important to further improve RF device characteristics of Ga2O3 MOSFETs.

    DOI: 10.1063/5.0029530

  • Reduction in leakage current through interface between Ga2O3 epitaxial layer and substrate by ion implantation doping of compensating impurities

    Sandeep Kumar, Takafumi Kamimura, Chia-Hung Lin, Yoshiaki Nakata, Masataka Higashiwaki

    APPLIED PHYSICS LETTERS   117 ( 19 )   2020.11( ISSN:0003-6951

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    Strong accumulation of Si impurities has been observed at a Ga2O3 epilayer/substrate interface. The highly Si-doped region around the interface typically becomes a current conduction path, causing buffer leakage for lateral Ga2O3 field-effect transistors (FETs). To overcome the drawback, we performed Mg- or Fe-ion implantation doping into a Ga2O3 substrate prior to the subsequent molecular-beam epitaxy growth to compensate the accumulated Si donors at the interface. The Mg implantation doping showed a minimal effect on reduction in the interface leakage, irrespective of its concentration. On the other hand, the Fe doping with a high density of 2x10(19)cm(-3) provided a significant decrease in the leakage and decent FET characteristics.

    DOI: 10.1063/5.0029286

  • Vertical beta-Ga2O3 Power Transistors: A Review

    Man Hoi Wong, Masataka Higashiwaki

    IEEE TRANSACTIONS ON ELECTRON DEVICES   67 ( 10 )   3925 - 3937   2020.10( ISSN:0018-9383

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    With projected performance advantages over silicon and incumbent wide-bandgap compound semiconductors, gallium oxide (Ga2O3) has garnered worldwide attention as an ultrawide-bandgap semiconductor material suitable for high-voltage, high-temperature, and radiation-hard electronics. Thanks to recent breakthroughs in crystal growth and device processing technologies, the research and development of vertically oriented Ga2O3 power transistors has made rapid strides. In this article, we review the important engineering achievements and performance milestones of the two major types of vertical Ga2O3 transistors-current aperture vertical metal-oxide-semiconductor field-effect transistors (MOSFETs) and vertical fin-channel MOSFETs. Challenges underlying the unique processing approaches to these devices and their implications on device reliability are also discussed.

    DOI: 10.1109/TED.2020.3016609

  • Vertical Gallium Oxide Transistors with Current Aperture Formed Using Nitrogen-Ion Implantation Process

    Higashiwaki M.

    4th Electron Devices Technology and Manufacturing Conference, EDTM 2020 - Proceedings   2020.04( ISBN:9781728125381

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  • Comment on “Characteristics of Multi-photon Absorption in a β-Ga2O3 Single Crystal” [J. Phys. Soc. Jpn. 88, 113701 (2019)]

    Rafał Korlacki, Alyssa Mock, Chad Briley, Vanya Darakchieva, Bo Monemar, Yoshinao Kumagai, Ken Goto, Masataka Higashiwaki, Mathias Schubert

    Journal of the Physical Society of Japan   89 ( 3 )   036001 - 036001   2020.03( ISSN:0031-9015

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    DOI: 10.7566/jpsj.89.036001

  • Enhancement-Mode $\beta$ -Ga2O3 Current Aperture Vertical MOSFETs With N-Ion-Implanted Blocker

    Man Hoi Wong, Hisashi Murakami, Yoshinao Kumagai, Masataka Higashiwaki

    IEEE Electron Device Letters   41 ( 2 )   296 - 299   2020.02( ISSN:0741-3106

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    Enhancement-mode (E-mode) vertical beta-Ga2O3 metal-oxide-semiconductor (MOS) field-effect transistors featuring a current aperture were developed on a single-crystal beta-Ga2O3 (001) substrate. Nitrogen ions were implanted into a drift layer grown by halide vapor phase epitaxy to form current blocking layers (CBLs) for vertical source-drain isolation, while Si ionswere implanted to form degenerately doped source contact regions and a top-gated lateral channel that was fully depleted at 0-V gate bias. The devices delivered a high output current on/off ratio of 2x10(7) despite a nonideal MOS interface that limited the maximum drain current density to <0.1 kA/cm(2). Pulsed operation without current collapse under off-state voltage stress was demonstrated. Hard breakdown occurred prematurely owing to leakage through the CBLs, but is expected to improve with an optimized nitrogen implantation process. The realization of E-mode vertical Ga2O3 transistors based on a manufacturable all-ion-implanted process represents an important step toward practical applications of Ga2O3 power electronics.

    DOI: 10.1109/led.2019.2962657

  • Preface

    Hideto Miyake, Masakazu Sugiyama, Yasuyuki Miyamoto, Masakazu Arai, Kazuhide Kumakura, Shugo Nitta, Munetaka Arita, Ryuji Katayama, Toshifumi Irisawa, Masataka Higashiwaki, Katsuhiro Tomioka

    JOURNAL OF CRYSTAL GROWTH   531   2020.02( ISSN:0022-0248

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    Publishing type:Research paper (scientific journal)  

    DOI: 10.1016/j.jcrysgro.2019.125337

  • Preface

    Hideto Miyake, Masakazu Sugiyama, Yasuyuki Miyamoto, Masakazu Arai, Kazuhide Kumakura, Shugo Nitta, Munetaka Arita, Ryuji Katayama, Toshifumi Irisawa, Masataka Higashiwaki, Katsuhiro Tomioka

    JOURNAL OF CRYSTAL GROWTH   532   2020.02( ISSN:0022-0248

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    DOI: 10.1016/j.jcrysgro.2019.125427

  • Preface

    Higashiwaki, M., Fujita, S.

    Springer Series in Materials Science   293   v - vi   2020( ISSN:0933033X

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  • Field-effect transistors 2: Ga<sub>2</sub>O<sub>3</sub> field-effect transistors for power switching and radiation-hard electronics

    Wong, M.H., Higashiwaki, M.

    Springer Series in Materials Science   293   583 - 607   2020( ISSN:2196-2812

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    Publishing type:Research paper (scientific journal)  

    DOI: 10.1007/978-3-030-37153-1_32

  • Introduction

    Higashiwaki, M.

    Springer Series in Materials Science   293   1 - 12   2020( ISSN:2196-2812

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    DOI: 10.1007/978-3-030-37153-1_1

  • Phonon properties: Phonon and free charge carrier properties in monoclinic-symmetry β-Ga<sub>2</sub>O<sub>3</sub>

    Schubert, M., Mock, A., Korlacki, R., Knight, S., Monemar, B., Goto, K., Kumagai, Y., Kuramata, A., Galazka, Z., Wagner, G., Tadjer, M.J., Wheeler, V.D., Higashiwaki, M., Darakchieva, V.

    Springer Series in Materials Science   293   501 - 534   2020( ISSN:2196-2812

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    Publishing type:Research paper (scientific journal)  

    DOI: 10.1007/978-3-030-37153-1_28

  • Vertical Gallium Oxide Transistors with Current Aperture Formed Using Nitrogen-Ion Implantation Process

    Masataka Higashiwaki, Man Hoi Wong, Ken Goto, Hisashi Murakami, Yoshinao Kumagai

    2020 IEEE ELECTRON DEVICES TECHNOLOGY AND MANUFACTURING CONFERENCE (EDTM 2020)   2020

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    Publishing type:Research paper (international conference proceedings)  

    Gallium oxide (Ga2O3) is an attractive material for next-generation power device applications due to its large breakdown electric field (>7 MV/cm). This paper highlights current-aperture vertical Ga2O3 metal-oxide-semiconductor field-effect transistors fabricated using silicon- and nitrogen-ion implantation processes.

  • Charge trapping and degradation of Ga<inf>2</inf>O<inf>3</inf> isolation structures for power electronics

    De Santi C.

    Proceedings of SPIE - The International Society for Optical Engineering   11281   2020( ISSN:0277786X ( ISBN:9781510633254

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  • Electroreflectance study on optical anisotropy in beta-Ga2O3

    Onuma, T., Tanaka, K., Sasaki, K., Yamaguchi, T., Honda, T., Kuramata, A., Yamakoshi, S., Higashiwaki, M.

    Applied Physics Letters   115 ( 23 )   2019.12( ISSN:00036951

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    Publishing type:Research paper (scientific journal)  

    DOI: 10.1063/1.5123985

  • Invited: Process and Characterization of Vertical Ga<inf>2</inf>O<inf>3</inf> Transistors

    Higashiwaki M.

    IMFEDK 2019 - International Meeting for Future of Electron Devices, Kansai   67 - 68   2019.11( ISBN:9781728131627

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  • Stability and degradation of isolation and surface in Ga2O3 devices

    C. De Santi, A. Nardo, M.H. Wong, K. Goto, A. Kuramata, S. Yamakoshi, H. Murakami, Y. Kumagai, M. Higashiwaki, G. Meneghesso, E. Zanoni, M. Meneghini

    Microelectronics Reliability   100-101   113453 - 113453   2019.09( ISSN:0026-2714

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    DOI: 10.1016/j.microrel.2019.113453

  • Vertical Ga2O3 Schottky Barrier Diodes With Guard Ring Formed by Nitrogen-Ion Implantation Reviewed

    Lin Chia-Hung, Yuda Yohei, Wong Man Hoi, Sato Mayuko, Takekawa Nao, Konishi Keita, Watahiki Tatsuro, Yamamuka Mikio, Murakami Hisashi, Kumagai Yoshinao, Higashiwaki Masataka

    IEEE ELECTRON DEVICE LETTERS   40 ( 9 )   1487 - 1490   2019.09( ISSN:0741-3106

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    A guard ring (GR) was employed to improve the breakdown voltage (V-br) of vertical Ga(2)O(3 )Schottky barrier diodes (SBDs) with or without a field-plate (FP) by eliminating electric field concentration at the edges of anode and FP electrodes. The GR structure was formed by nitrogen (N)-ion implantation. Four types of vertical SBD structures with: 1) neither a GR nor a FP; 2) a GR; 3) a FP; and 4) both a GR and a FP were fabricated on the same substrate. The SBDs with a GR [structures 2) and 4)] showed larger V-br values than their GR-free counterparts [structures 1) and 3)]. Considering the trade-off relationship between V-br and specific on-resistance (R-on), a V-br/R-on combination of 1.43 kV/4.7 m Omega.cm(2) for the GR/FP-SBD corresponds to one of the best balanced data for Ga2O3 SBDs.

    DOI: 10.1109/LED.2019.2927790

  • Normally-Off Ga2O3 MOSFETs With Unintentionally Nitrogen-Doped Channel Layer Grown by Plasma-Assisted Molecular Beam Epitaxy Reviewed

    Kamimura Takafumi, Nakata Yoshiaki, Wong Man Hoi, Higashiwaki Masataka

    IEEE ELECTRON DEVICE LETTERS   40 ( 7 )   1064 - 1067   2019.07( ISSN:0741-3106

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    We found that nitrogen (N) and silicon (Si) were unintentionally co-doped in Ga2O3 layers grown by plasma-assisted molecular beam epitaxy (PAMBE), and that the ratio between N and Si could be controlled by O/Ga flux ratio during the growth. Note that N and Si act as a deep acceptor (theoretically predicted) and a shallow donor (experimentally confirmed) in Ga2O3, respectively. Taking advantage of this unique characteristic of PAMBE-grown Ga2O3, normally off operation of Ga2O3 metal-oxide-semiconductor field-effect transistors (MOSFETs) was demonstrated. The unintentionally-doped-Ga2O3 channel layer of the MOSFETs had N and Si concentrations of 1 x 10(18) and 2 x 10(17) cm(-3), respectively, and thus it was considered to behave as a p-type material. The MOSFETs showed a turn-on threshold gate voltage of larger than + 8 V, implying formation of an inversion channel in the N-doped Ga2O3 layer. Although the ON-state drain current (I-d) remained in the subthreshold regime owing to limited gate voltage swing, the I-d ON/OFF ratio exceeded five orders of magnitude.

    DOI: 10.1109/LED.2019.2919251

  • Enhancement-Mode Current Aperture Vertical GaO MOSFETs

    Wong M.H.

    Device Research Conference - Conference Digest, DRC   2019-June   225 - 226   2019.06( ISSN:15483770 ( ISBN:9781728121123

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  • Observation of Electroreflectance Spectra of β-Ga<inf>2</inf>O<inf>3</inf> Single Crystal

    Onuma T.

    2019 Compound Semiconductor Week, CSW 2019 - Proceedings   2019.05( ISBN:9781728100807

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  • Gallium Oxide Field Effect Transistors-Establishing New Frontiers of Power Switching and Radiation-Hard Electronics

    Wong, M.H., Higashiwaki, M.

    International Journal of High Speed Electronics and Systems   28 ( 1-2 )   2019.03( ISSN:01291564

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    Publishing type:Research paper (scientific journal)  

    DOI: 10.1142/S0129156419400020

  • Current ApertureCurrent Aperture Vertical beta-Ga2O3 MOSFETs Fabricated by N- and Si-Ion Implantation Doping Vertical <inline-formula> <tex-math notation="LaTeX">$\beta$ </tex-math> </inline-formula>-Ga2O3 MOSFETs Fabricated by N- and Si-Ion Implantation Reviewed

    Man Hoi Wong, Ken Goto, Hisashi Murakami, Yoshinao Kumagai, Masataka Higashiwaki

    IEEE Electron Device Letters   40 ( 3 )   431 - 434   2019.03( ISSN:0741-3106

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    Depletion-mode vertical Ga2O3 metal-oxidesemiconductor field-effect transistors featuring a current aperture were developed on a halide vapor phase epitaxial drift layer grown on a bulk beta-Ga2O3 (001) substrate. Three ion implantation steps were employed to fabricate the n ++ source regions, lateral n channel, and p current blocking layers, where Si and N were selected as the donor and deep acceptor dopant species, respectively. The transistors delivered a drain current density of 0.42 kA/cm(2), a specific on-resistance of 31.5m Omega.cm(2), and an output current on/off ratio of over 108. High-voltage performance of the present devices was hampered by a large gate oxide field in the off-state causing high gate leakage, a limitation that can be readily overcome through optimized doping schemes and an improved gate dielectric. The demonstration of a planar-gate vertical Ga2O3 transistor based on a highly manufacturable all-ion-implanted process greatly enhances the prospects for Ga2O3-based power electronics.

    DOI: 10.1109/LED.2018.2884542

  • Raman Thermography of Peak Channel Temperature in beta-Ga2O3 MOSFETs Reviewed

    Pomeroy J. W, Middleton C, Singh M, Dalcanale S, Uren M. J, Wong M. H, Sasaki K, Kuramata A, Yamakoshi S, Higashiwaki M, Kuball M

    IEEE Electron Device Letters   40 ( 2 )   189 - 192   2019.02( ISSN:07413106

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    DOI: 10.1109/LED.2018.2887278

  • Wide bandgap oxides

    Kevin D. Leedy, Kookrin Char, Masataka Higashiwaki, Rebecca L. Peterson, James S. Speck

    APL MATERIALS   7 ( 2 )   2019.02( ISSN:2166-532X

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    Publishing type:Research paper (scientific journal)  

    DOI: 10.1063/1.5091688

  • Nitrogen-Doped Channel beta-Ga2O3 MOSFET with Normally-Off Operation

    Takafumi Kamimura, Yoshiaki Nakata, Man Hoi Wong, Phuc Hong Than, Masataka Higashiwaki

    2019 COMPOUND SEMICONDUCTOR WEEK (CSW)   2019

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    Publishing type:Research paper (international conference proceedings)  

  • Invited: Process and Characterization of Vertical Ga2O3 Transistors

    Masataka Higashiwaki, Man Hoi Wong, Ken Goto, Hisashi Murakami, Yoshinao Kumagai

    2019 IEEE INTERNATIONAL MEETING FOR FUTURE OF ELECTRON DEVICES, KANSAI (IMFEDK2019)   67 - 68   2019

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    Gallium oxide (Ga2O3) is an emerging ultra-wide-bandgap semiconductor especially suitable for high-power and/or high-voltage switching device applications. In this paper, device fabrication process and characteristics of depletion-mode and enhancement-mode vertical Ga2O3 transistors fabricated by using a multiple ion-implantation doping process are discussed.

  • Dynamic R-ON in beta-Ga2O3 MOSFET Power Devices

    Taylor Moule, Manikant Singh, James Pomeroy, Serge Karboyan, Michael J. Uren, Man I. Loi Wong, Kohei Sasaki, Akito Kuramata, Shigenobu Yamakoshi, Masataka Higashiwaki, Martin Kuball

    2019 COMPOUND SEMICONDUCTOR WEEK (CSW)   2019

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  • beta-Ga2O3 MOSFETs with Nitrogen-Ion-Implanted Back-Barrier: DC Performance and Trapping Effects

    Man Hoi Wong, Ken Goto, Hisashi Murakami, Yoshinao Kumagai, Masataka Higashiwaki

    2019 COMPOUND SEMICONDUCTOR WEEK (CSW)   2019

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    Publishing type:Research paper (international conference proceedings)  

  • MBE growth and device applications of Ga<sub>2</sub>O<sub>3</sub>

    Higashiwaki, M.

    Molecular Beam Epitaxy: Materials and Applications for Electronics and Optoelectronics   411 - 422   2019( ISBN:9781119355021

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    Publishing type:Research paper (scientific journal)  

    DOI: 10.1002/9781119354987.ch25

  • Observation of Electroreflectance Spectra of beta-Ga2O3 Single Crystal

    Takcyoshi Onuma, Kouya Tanaka, Kohci Sasaki, Tomohiro Yamaguchi, Tohru Honda, Akito Kuramata, Shigenobu Yamakoshi, Masataka Higashiwaki

    2019 COMPOUND SEMICONDUCTOR WEEK (CSW)   2019

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    Electroreflectance (ER) spectra were measured using the Schottky barrier diodes. The ER spectra were well fitted by three components of exciton lineshape functions. The transition energies exhibited moderate changes with the external reverse bias by reflecting the broadening of the absorption edge. The results demonstrate the ER measurement is applicable for Ga2O3 and related alloys as a useful tool to investigate their band structure.

  • Vertical Ga2O3 Schottky Barrier Diodes with Guard Ring Formed by Nitrogen-Ion Implantation

    Chia-Hung Lin, Yohei Yuda, Man Hoi Wong, Mayuko Sato, Nao Takekawa, Keita Konishi, Tatsuro Watahiki, Mikio Yamamuka, Hisashi Murakami, Yoshinao Kumagai, Masataka Higashiwaki

    2019 COMPOUND SEMICONDUCTOR WEEK (CSW)   2019

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  • Single-crystal-Ga2O3/polycrystalline-SiC bonded substrate with low thermal and electrical resistances at the heterointerface Reviewed

    Lin Chia-Hung, Hatta Naoki, Konishi Keita, Watanabe Shinya, Kuramata Akito, Yagi Kuniaki, Higashiwaki Masataka

    Applied Physics Letters   114 ( 3 )   2019( ISSN:0003-6951

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    A single-crystal beta-Ga2O3 substrate was directly attached to a polycrystalline SiC (poly-SiC) substrate using a surface-activated-bonding method to enhance heat extraction from beta-Ga2O3 devices. The effective thermal conductivity of the n(+)-Ga2O3/n(+)-poly-SiC bonded substrate and the electrical resistance at the heterointerface were characterized by using periodic heating radiation thermometry and analyzing vertical current-voltage characteristics, respectively. Small thermal and electrical resistances at the bonded interface demonstrated the strong prospects of the bonded substrates for applications to high-power vertical Ga2O3 devices. Published under license by AIP Publishing.

    DOI: 10.1063/1.5051720

  • Halide vapor phase epitaxy of Si doped beta-Ga2O3 and its electrical properties Reviewed

    Goto Ken, Konishi Keita, Murakami Hisashi, Kumagai Yoshinao, Monemar Bo, Higashiwaki Masataka, Kuramata Akito, Yamakoshi Shigenobu

    Thin Solid Films   666   182 - 184   2018.11( ISSN:0040-6090

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    Silicon doped homoepitaxial films were grown on beta-gallium oxide (001) substrates by halide vapor phase epitaxy using gallium monochloride, oxygen and silicon tetrachloride gases as precursors. It was confirmed that the n-type carrier density at room temperature was almost equal to the doped silicon concentration, which was controlled in the range of 10(15) to 10(18) cm(-3). In the doped film with the carrier density of 1x10(16) cm(-3), the activation energy and the mobility at room temperature were 45.6 meV and 145 cm(2)/V.s, respectively. The carrier scattering mechanism in the low carrier density film was dominated by optical phonon scattering with the phonon energy of 33 meV. These results suggest that the doped homoepitaxial film grown by halide vapor phase epitaxy is a high quality film with good crystallinity comparable to bulk crystals.

    DOI: 10.1016/j.tsf.2018.09.006

  • Pulsed Large Signal RF Performance of Field-Plated Ga2O3 MOSFETs Reviewed

    Singh Manikant, Casbon Michael A, Uren Michael J, Pomeroy James W, Dalcanale Stefano, Karboyan Serge, Tasker Paul J, Wong Man Hoi, Sasaki Kohei, Kuramata Akito, Yamakoshi Shigenobu, Higashiwaki Masataka, Kuball Martin

    IEEE ELECTRON DEVICE LETTERS   39 ( 10 )   1572 - 1575   2018.10( ISSN:0741-3106

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    Comparison between pulsed and CW large signal RF performance of field-plated beta-Ga2O3 MOSFETs has been reported. Reduced self-heating when pulse resulted in a power added efficiency of 12%, drain efficiency of 22.4%, output power density of 0.13 W/mm, and maximum gain up to 4.8 dB at 1 GHz for a 2-mu m gate length device. Increased power dissipation for higher V-DS and I-DS resulted in a degradation in performance, which, thermal simulation showed, could be entirely explained by self-heating. Buffer and surface trapping contributions have been evaluated using gate and drain lag measurements, showing minimal impact on device performance. These results suggest that beta-Ga2O3 is a good candidate for future RF applications.

    DOI: 10.1109/LED.2018.2865832

  • Acceptor doping of beta-Ga2O3 by Mg and N ion implantations Reviewed

    Wong Man Hoi, Lin Chia-Hung, Kuramata Akito, Yamakoshi Shigenobu, Murakami Hisashi, Kumagai Yoshinao, Higashiwaki Masataka

    APPLIED PHYSICS LETTERS   113 ( 10 )   2018.09( ISSN:0003-6951

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    Deep acceptor doping of beta-Ga2O3 with Mg and N was demonstrated by implantation of the impurity ions into n-type bulk substrates. Systematic physical and electrical characterizations were performed to demonstrate recovery of the implantation-damaged crystals and electrical activation of the dopant atoms by thermal annealing at 1000-1200 degrees C in an N-2 atmosphere. N was found to exhibit much lower thermal diffusivity than Mg, thus enabling the use of higher annealing temperatures to maximize N activation efficiency without significantly altering the impurity profile. Consequently, an n-Ga2O3 /Ga2O3:N/n-Ga2O3 structure was capable of sustaining a much larger voltage across its end terminals than its Mg-doped counterpart. The development of an ion implantation technology for acceptor doping of beta-Ga2O3 creates unique opportunities for designing and engineering a variety of high-voltage beta-Ga(2)O(3 )devices. Published by AIP Publishing.

    DOI: 10.1063/1.5050040

  • Comparison of O2 and H2O as oxygen source for homoepitaxial growth of β-Ga2O3 layers by halide vapor phase epitaxy Reviewed

    Keita Konishi, Ken Goto, Rie Togashi, Hisashi Murakami, Masataka Higashiwaki, Akito Kuramata, Shigenobu Yamakoshi, Bo Monemar, Yoshinao Kumagai

    Journal of Crystal Growth   492   39 - 44   2018.06( ISSN:0022-0248

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    Homoepitaxial growth of β-Ga2O3 layers by halide vapor phase epitaxy (HVPE) using O2 or H2O as an oxygen source was investigated by thermodynamic analysis, and compared with measured properties after growth. The thermodynamic analysis revealed that Ga2O3 growth is expected even at 1000 °C using both oxygen sources due to positive driving forces for Ga2O3 deposition. The experimental results for homoepitaxial growth on (0 0 1) β-Ga2O3 substrates showed that the surfaces of the layers grown with H2O were smoother than those grown with O2, although the growth rate with H2O was approximately half that with O2. However, in the homoepitaxial layer grown using H2O, incorporation of Si impurities with a concentration almost equal to the effective donor concentration (2 × 1016 cm−3) was confirmed, which was caused by decomposition of the quartz glass reactor due to the presence of hydrogen in the system.

    DOI: 10.1016/j.jcrysgro.2018.04.009

  • Optical signatures of deep level defects in Ga2O3 Reviewed

    Hantian Gao, Shreyas Muralidharan, Nicholas Pronin, Md Rezaul Karim, Susan M. White, Thaddeus Asel, Geoffrey Foster, Sriram Krishnamoorthy, Siddharth Rajan, Lei R. Cao, Masataka Higashiwaki, Holger Von Wenckstern, Marius Grundmann, Hongping Zhao, David C. Look, Leonard J. Brillson

    Applied Physics Letters   112 ( 24 )   2018.06( ISSN:0003-6951

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    We used depth-resolved cathodoluminescence spectroscopy and surface photovoltage spectroscopy to measure the effects of near-surface plasma processing and neutron irradiation on native point defects in β-Ga2O3. The near-surface sensitivity and depth resolution of these optical techniques enabled us to identify spectral changes associated with removing or creating these defects, leading to identification of one oxygen vacancy-related and two gallium vacancy-related energy levels in the β-Ga2O3 bandgap. The combined near-surface detection and processing of Ga2O3 suggests an avenue for identifying the physical nature and reducing the density of native point defects in this and other semiconductors.

    DOI: 10.1063/1.5026770

  • All-ion-implanted planar-gate current aperture vertical Ga2O3 MOSFETs with Mg-doped blocking layer Reviewed

    Man Hoi Wong, Ken Goto, Yoji Morikawa, Akito Kuramata, Shigenobu Yamakoshi, Hisashi Murakami, Yoshinao Kumagai, Masataka Higashiwaki

    Applied Physics Express   11 ( 6 )   2018.06( ISSN:1882-0786

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    A vertical β-Ga2O3 metal-oxide-semiconductor field-effect transistor featuring a planar-gate architecture is presented. The device was fabricated by an all-ion-implanted process without requiring trench etching or epitaxial regrowth. A Mg-ion-implanted current blocking layer (CBL) provided electrical isolation between the source and the drain except at an aperture opening through which drain current was conducted. Successful transistor action was realized by gating a Si-ion-implanted channel above the CBL. Thermal diffusion of Mg induced a large source-drain leakage current through the CBL, which resulted in compromised off-state device characteristics as well as a reduced peak extrinsic transconductance compared with the results of simulations.

    DOI: 10.7567/APEX.11.064102

  • Relation Between Electrical and Optical Properties of p-Type NiO Films Reviewed

    Mizuki Ono, Kohei Sasaki, Hiroki Nagai, Tomohiro Yamaguchi, Masataka Higashiwaki, Akito Kuramata, Shigenobu Yamakoshi, Mitsunobu Sato, Tohru Honda, Takeyoshi Onuma

    Physica Status Solidi (B) Basic Research   255 ( 4 )   2018.04( ISSN:0370-1972

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    © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Relation between the electrical and optical properties of p-type NiO films prepared either by RF sputtering or by the molecular precursor method is studied in terms of changes in crystallinity, resistivity ρ and absorption coefficients α. Values of α are correlated with electronic structures near the valence band maximum, which are obtained from the X-ray photoelectron spectroscopy measurements and the density functional theory calculations. The ρ and α values are found to be strongly influenced by the crystallinity as well as the Ni vacancies as acceptor-type intrinsic point defects.

    DOI: 10.1002/pssb.201700311

  • Guest Editorial: The dawn of gallium oxide microelectronics Reviewed

    Masataka Higashiwaki, Gregg H. Jessen

    Applied Physics Letters   112 ( 6 )   2018.02( ISSN:0003-6951

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    DOI: 10.1063/1.5017845

  • Radiation hardness of β -Ga2O3 metal-oxide-semiconductor field-effect transistors against gamma-ray irradiation Reviewed

    Man Hoi Wong, Akinori Takeyama, Takahiro Makino, Takeshi Ohshima, Kohei Sasaki, Akito Kuramata, Shigenobu Yamakoshi, Masataka Higashiwaki

    Applied Physics Letters   112 ( 2 )   2018.01( ISSN:0003-6951

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    The effects of ionizing radiation on β-Ga2O3 metal-oxide-semiconductor field-effect transistors (MOSFETs) were investigated. A gamma-ray tolerance as high as 1.6 MGy(SiO2) was demonstrated for the bulk Ga2O3 channel by virtue of weak radiation effects on the MOSFETs' output current and threshold voltage. The MOSFETs remained functional with insignificant hysteresis in their transfer characteristics after exposure to the maximum cumulative dose. Despite the intrinsic radiation hardness of Ga2O3, radiation-induced gate leakage and drain current dispersion ascribed respectively to dielectric damage and interface charge trapping were found to limit the overall radiation hardness of these devices.

    DOI: 10.1063/1.5017810

  • Ultrawide-Bandgap Semiconductors: Research Opportunities and Challenges Reviewed

    J. Y. Tsao, S. Chowdhury, M. A. Hollis, D. Jena, N. M. Johnson, K. A. Jones, R. J. Kaplar, S. Rajan, C. G. Van de Walle, E. Bellotti, C. L. Chua, R. Collazo, M. E. Coltrin, J. A. Cooper, K. R. Evans, S. Graham, T. A. Grotjohn, E. R. Heller, M. Higashiwaki, M. S. Islam, P. W. Juodawlkis, M. A. Khan, A. D. Koehler, J. H. Leach, U. K. Mishra, R. J. Nemanich, R. C.N. Pilawa-Podgurski, J. B. Shealy, Z. Sitar, M. J. Tadjer, A. F. Witulski, M. Wraback, J. A. Simmons

    Advanced Electronic Materials   4 ( 1 )   2018.01( ISSN:2199-160X

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    Ultrawide-bandgap (UWBG) semiconductors, with bandgaps significantly wider than the 3.4 eV of GaN, represent an exciting and challenging new area of research in semiconductor materials, physics, devices, and applications. Because many figures-of-merit for device performance scale nonlinearly with bandgap, these semiconductors have long been known to have compelling potential advantages over their narrower-bandgap cousins in high-power and RF electronics, as well as in deep-UV optoelectronics, quantum information, and extreme-environment applications. Only recently, however, have the UWBG semiconductor materials, such as high Al-content AlGaN, diamond and Ga2O3, advanced in maturity to the point where realizing some of their tantalizing advantages is a relatively near-term possibility. In this article, the materials, physics, device and application research opportunities and challenges for advancing their state of the art are surveyed.

    DOI: 10.1002/aelm.201600501

  • Electron effective mass in Sn-doped monoclinic single crystal β-gallium oxide determined by mid-infrared optical Hall effect Reviewed

    Sean Knight, Alyssa Mock, Rafał Korlacki, Vanya Darakchieva, Bo Monemar, Yoshinao Kumagai, Ken Goto, Masataka Higashiwaki, Mathias Schubert

    Applied Physics Letters   112 ( 1 )   2018.01( ISSN:0003-6951

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    The isotropic average conduction band minimum electron effective mass in Sn-doped monoclinic single crystal β-Ga2O3 is experimentally determined by the mid-infrared optical Hall effect to be (0.284 ± 0.013)m0 combining investigations on (010) and (2-01) surface cuts. This result falls within the broad range of values predicted by theoretical calculations for undoped β-Ga2O3. The result is also comparable to recent density functional calculations using the Gaussian-attenuation-Perdew-Burke-Ernzerhof hybrid density functional, which predict an average effective mass of 0.267m0. Within our uncertainty limits, we detect no anisotropy for the electron effective mass, which is consistent with most previous theoretical calculations. We discuss upper limits for possible anisotropy of the electron effective mass parameter from our experimental uncertainty limits, and we compare our findings with recent theoretical results.

    DOI: 10.1063/1.5011192

  • Latest progress in gallium-oxide electronic devices Reviewed

    Masataka Higashiwaki, Man Hoi Wong, Keita Konishi, Yoshiaki Nakata, Chia-Hung Lin, Takafumi Kamimura, Lingaparthi Ravikiran, Kohei Sasaki, Ken Goto, Akinori Takeyama, Takahiro Makino, Takeshi Ohshima, Akito Kuramata, Shigenobu Yamakoshi, Hisashi Murakami, Yoshinao Kumagai

    Proceedings of SPIE - The International Society for Optical Engineering   10533   2018( ISSN:1996-756X

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    Gallium oxide (Ga2O3) has emerged as a new competitor to SiC and GaN in the race toward next-generation power switching and harsh environment electronics by virtue of the excellent material properties and the relative ease of mass wafer production. In this proceedings paper, an overview of our recent development progress of Ga2O3 metal-oxide-semiconductor field-effect transistors and Schottky barrier diodes will be reported.

    DOI: 10.1117/12.2292666

  • Modeling and interpretation of UV and blue luminescence intensity in beta-Ga2O3 by silicon and nitrogen doping Reviewed

    Onuma T, Nakata Y, Sasaki K, Masui T, Yamaguchi T, Honda T, Kuramata A, Yamakoshi S, Higashiwaki M

    Journal of Applied Physics   124 ( 7 )   2018

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    DOI: 10.1063/1.5030612

  • Recent Advances in Ga2O3 MOSFET Technologies Reviewed

    Higashiwaki Masataka, Wong Man Hoi, Kamimura Takafumi, Nakata Yoshiaki, Lin Chia-Hung, Lingaparthi Ravikiran, Takeyama Akinori, Makino Takahiro, Ohshima Takeshi, Hatta Naoki, Yagi Kuniaki, Goto Ken, Sasaki Kohei, Watanabe Shinya, Kuramata Akito, Yamakoshi Shigenobu, Konishi Keita, Murakami Hisashi, Kumagai Yoshinao, IEEE

    2018 76th Device Research Conference (Drc)   2018( ISSN:1548-3770

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  • Relation Between Electrical and Optical Properties of p-Type NiO Films Reviewed

    Ono, M, Sasaki, K, Nagai, H, Yamaguchi, T, Higashiwaki, M, Kuramata, A, Yamakoshi, S, Sato, M, Honda, T, Onuma, T

    Physica Status Solidi (B) Basic Research   255 ( 4 )   2018( ISSN:2079-6412

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  • Band-to-band transitions, selection rules, effective mass, and excitonic contributions in monoclinic beta-Ga2O3 Reviewed

    Alyssa Mock, Rafal Korlacki, Chad Briley, Vanya Darakchieva, Bo Monemar, Yoshinao Kumagai, Ken Goto, Masataka Higashiwaki, Mathias Schubert

    PHYSICAL REVIEW B   96 ( 24 )   2017.12( ISSN:2469-9950

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    We employ an eigenpolarization model including the description of direction dependent excitonic effects for rendering critical point structures within the dielectric function tensor of monoclinic beta-Ga2O3 yielding a comprehensive analysis of generalized ellipsometry data obtained from 0.75-9 eV. The eigenpolarization model permits complete description of the dielectric response. We obtain, for single-electron and excitonic band-to-band transitions, anisotropic critical point model parameters including their polarization vectors within the monoclinic lattice. We compare our experimental analysis with results from density functional theory calculations performed using the Gaussian-attenuation-Perdew-Burke-Ernzerhof hybrid density functional. We present and discuss the order of the fundamental direct band-to-band transitions and their polarization selection rules, the electron and hole effective mass parameters for the three lowest band-to-band transitions, and their excitonic contributions. We find that the effective masses for holes are highly anisotropic and correlate with the selection rules for the fundamental band-to-band transitions. The observed transitions are polarized close to the direction of the lowest hole effective mass for the valence band participating in the transition.

    DOI: 10.1103/PhysRevB.96.245205

  • State-of-the-art technologies of gallium oxide power devices Reviewed

    Masataka Higashiwaki, Akito Kuramata, Hisashi Murakami, Yoshinao Kumagai

    JOURNAL OF PHYSICS D-APPLIED PHYSICS   50 ( 33 )   2017.08( ISSN:0022-3727

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    Gallium oxide (Ga2O3) has gained increased attention for power devices due to its superior material properties and the availability of economical device-quality native substrates. This review illustrates recent advances in Ga2O3 device technologies, beginning with an overview of the social circumstances that motivate the development of new-generation switching devices. Following an introduction to the material properties of Ga2O3 from the viewpoint of power electronics, growth technologies of Ga2O3 bulk single crystals and epitaxial thin films are discussed. The fabrication and performance of state-of-the-art Ga2O3 transistors and diodes are then described. We conclude by identifying the directions and challenges of Ga2O3 power device development in the near future.

    DOI: 10.1088/1361-6463/aa7aff

  • First Demonstration of Ga2O3 Trench MOS-Type Schottky Barrier Diodes Reviewed

    Kohei Sasaki, Daiki Wakimoto, Quang Tu Thieu, Yuki Koishikawa, Akito Kuramata, Masataka Higashiwaki, Shigenobu Yamakoshi

    IEEE ELECTRON DEVICE LETTERS   38 ( 6 )   783 - 785   2017.06( ISSN:0741-3106

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    We developed beta-Ga2O3 trench MOS-type Schottky barrier diodes (MOSSBDs) for the first time. A Si-doped Ga2O3 layer was grown via halide vapor phase epitaxy on a single-crystal Sn-doped beta-Ga2O3 (001) substrate. The trench structure was fabricated using dry etching and photolithography. HfO2 film was used as the dielectric film of the trench MOS structure. The specific on-resistances (R-ON, (SP)) of the normalSBDand trenchMOSSBDwere about 2.3 and 2.9 m Omega cm(2), respectively. The reason the R-ON, (SP) of MOSSBD was a little higher than that of the Schottky barrier diodes (SBD) is that the current path decrease as a result of forming the trench MOS structure. The normal SBD had a large reverse leakage current due to the large electricfield at the anodemetal/semiconductorinterface. On the other hand, the trench MOSSBD had several orders of magnitude smaller leakage current. We, thus, demonstrated that incorporating the trench MOS structure in Ga2O3 is highly effective for decreasing the reverse leakage current.

    DOI: 10.1109/LED.2017.2696986

  • Enhancement-mode Ga2O3 MOSFETs with Si-ion-implanted source and drain Reviewed

    Man Hoi Wong, Yoshiaki Nakata, Akito Kuramata, Shigenobu Yamakoshi, Masataka Higashiwaki

    APPLIED PHYSICS EXPRESS   10 ( 4 )   2017.04( ISSN:1882-0778

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    Enhancement-mode alpha-Ga2O3 metal-oxide-semiconductor field-effect transistors with low series resistance were achieved by Si-ion implantation doping of the source/drain contacts and access regions. An unintentionally doped Ga2O3 channel with low background carrier concentration that was fully depleted at a gate bias of 0 V gave rise to a positive threshold voltage without additional constraints on the channel dimensions or device architecture. Transistors with a channel length of 4 mu m delivered a maximum drain current density (I-DS) of 1.4mA/mm and an IDS on/off ratio near 10(6). Nonidealities associated with the Al2O3 gate dielectric as well as their impact on enhancement-mode device performance are discussed. (C) 2017 The Japan Society of Applied Physics

    DOI: 10.7567/APEX.10.041101

  • Smart Power Devices and ICs Using GaAs and Wide and Extreme Bandgap Semiconductors Reviewed

    T. Paul Chow, Ichiro Omura, Masataka Higashiwaki, Hiroshi Kawarada, Vipindas Pala

    IEEE TRANSACTIONS ON ELECTRON DEVICES   64 ( 3 )   856 - 873   2017.03( ISSN:0018-9383

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    We evaluate and compare the performance and potential of GaAs and of wide and extreme bandgap semiconductors (SiC, GaN, Ga2O3, and diamond), relative to silicon, for power electronics applications. We examine their device structures and associated materials/process technologies and selectively reviewthe recent experimental demonstrations of high voltage power devices and IC structures of these semiconductors. We discuss the technical obstacles that still need to be addressed and overcome before large-scale commercialization commences.

    DOI: 10.1109/TED.2017.2653759

  • 1-kV vertical Ga2O3 field-plated Schottky barrier diodes Reviewed

    Keita Konishi, Ken Goto, Hisashi Murakami, Yoshinao Kumagai, Akito Kuramata, Shigenobu Yamakoshi, Masataka Higashiwaki

    APPLIED PHYSICS LETTERS   110 ( 10 )   2017.03( ISSN:0003-6951

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    Ga2O3 field-plated Schottky barrier diodes (FP-SBDs) were fabricated on a Si-doped n(-)-Ga2O3 drift layer grown by halide vapor phase epitaxy on a Sn-doped n(+)-Ga2O3 (001) substrate. The specific on-resistance of the Ga2O3 FP-SBD was estimated to be 5.1 m Omega.cm(2). Successful field-plate engineering resulted in a high breakdown voltage of 1076 V. A larger-than-expected effective barrier height of 1.46 eV, which was extracted from the temperature-dependent current-voltage characteristics, could be caused by the effect of fluorine atoms delivered in a hydrofluoric acid solution process.

    DOI: 10.1063/1.4977857

  • Radiation Hardness of Ga2O3 MOSFETs Against Gamma-Ray Irradiation Reviewed

    Wong Man Hoi, Takeyama Akinori, Makino Takahiro, Ohshima Takeshi, Sasaki Kohei, Kuramata Akito, Yamakoshi Shigenobu, Higashiwaki Masataka, IEEE

    2017 75th Annual Device Research Conference (Drc)   2017( ISSN:1548-3770

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  • Demonstration of Ga2O3 Trench MOS-Type Schottky Barrier Diodes Reviewed

    Sasaki K, Wakimoto D, Thieu Q. T, Koishikawa Y, Kuramata A, Higashiwaki M, Yamakoshi S, IEEE

    2017 75th Annual Device Research Conference (Drc)   2017

  • First Demonstration of Vertical Ga2O3 MOSFET: Planar Structure with a Current Aperture Reviewed

    Wong Man Hoi, Goto Ken, Kuramata Akito, Yamakoshi Shigenobu, Murakami Hisashi, Kumagai Yoshinao, Higashiwaki Masataka, IEEE

    2017 75th Annual Device Research Conference (Drc)   2017( ISSN:1548-3770

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    DOI: 10.1109/DRC.2017.7999413

  • Spectroscopic ellipsometry studies on beta-Ga2O3 films and single crystal Reviewed

    Takeyoshi Onuma, Shingo Saito, Kohei Sasaki, Tatekazu Masui, Tomohiro Yamaguchi, Tohru Honda, Akito Kuramata, Masataka Higashiwaki

    JAPANESE JOURNAL OF APPLIED PHYSICS   55 ( 12 )   2016.12( ISSN:0021-4922

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    Anisotropic optical properties are investigated on beta-Ga2O3 films and a single crystal by spectroscopic ellipsometry measurements. The (2011) films grown on (0001) alpha-Al2O3 contain threefold in-plane rotational domains, and the refractive index and absorption coefficient a obtained by assuming an isotropic material are found to be smaller than those in the single crystal. By measuring the off-normal transmission ellipsometry spectra of the (010) beta-Ga2O3 substrate, the optical anisotropy in a biaxial crystal as well as the gradual increase in a are recognized as origins of the scattering in optically determined bandgap energies. (C) 2016 The Japan Society of Applied Physics

    DOI: 10.7567/JJAP.55.1202B2

  • Current status of Ga2O3 power devices Reviewed

    Masataka Higashiwaki, Hisashi Murakami, Yoshinao Kumagai, Akito Kuramata

    JAPANESE JOURNAL OF APPLIED PHYSICS   55 ( 12 )   2016.12( ISSN:0021-4922

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    Gallium oxide (Ga2O3) is an emerging wide-bandgap semiconductor for high-power, low-loss transistors and diodes by virtue of its excellent material properties and suitability for mass production. In this paper, we begin by discussing the material properties of Ga2O3 that make it an attractive alternative to not only Si but also other wide-bandgap materials such as SiC and GaN. State-of-the-art Ga2O3-based devices that have been fabricated to date demonstrate the performance potential for power electronics applications. (C) 2016 The Japan Society of Applied Physics

    DOI: 10.7567/JJAP.55.1202A1

  • Gallium Oxide and Related Semiconductors FOREWORD Reviewed

    Shizuo Fujita, Makoto Kasu, Masataka Higashiwaki, Yoshinao Kumagai, Takeyoshi Onuma, Takayoshi Oshima, Kazuyuki Uno

    JAPANESE JOURNAL OF APPLIED PHYSICS   55 ( 12 )   2016.12( ISSN:0021-4922

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    DOI: 10.7567/JJAP.55.120201

  • Epitaxially grown crystalline Al2O3 interlayer on beta-Ga2O3(010) and its suppressed interface state density Reviewed

    Takafumi Kamimura, Daivasigamani Krishnamurthy, Akito Kuramata, Shigenobu Yamakoshi, Masataka Higashiwaki

    JAPANESE JOURNAL OF APPLIED PHYSICS   55 ( 12 )   2016.12( ISSN:0021-4922

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    Al2O3 films were deposited on beta-Ga2O3(010) and beta-Ga2O3(201) substrates by atomic layer deposition at 250 degrees C, and their interface state densities (D-it) at shallow energies were evaluated using a high-low capacitance-voltage (C-V) method. Al2O3/beta-Ga2O3(010) showed lower D-it values (5.9 x 10(10) to 9.3 x 10(11)cm(-2)eV(-1)) than Al2O3/beta-Ga2O3(201) (2.0 x 10(11) to 2.0 x 10(12)cm(-2)eV(-1)) in an energy range of -0.8 to -0.1 eV. Cross-sectional transmission electron microscopy analysis indicated the formation of a uniform amorphous Al2O3 layer on the beta-Ga2O3(201) substrate. In contrast, a crystalline Al2O3 interlayer with a thickness of 3.2 +/- 0.7nm with an amorphous Al2O3 top layer was formed on the beta-Ga2O3(010) substrate, which effectively decreased D-it. Moreover, thicker interlayers showing lower D-it values at deep state levels were formed at deposition temperatures higher than 100 degrees C, which were evaluated by shifts in the C-V curves. (C) 2016 The Japan Society of Applied Physics

    DOI: 10.7567/JJAP.55.1202B5

  • Electronic properties of the residual donor in unintentionally doped beta-Ga2O3 Reviewed

    N. T. Son, K. Goto, K. Nomura, Q. T. Thieu, R. Togashi, H. Murakami, Y. Kumagai, A. Kuramata, M. Higashiwaki, A. Koukitu, S. Yamakoshi, B. Monemar, E. Janzen

    JOURNAL OF APPLIED PHYSICS   120 ( 23 )   2016.12( ISSN:0021-8979

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    Electron paramagnetic resonance was used to study the donor that is responsible for the n-type conductivity in unintentionally doped (UID) beta-Ga2O3 substrates. We show that in as-grown materials, the donor requires high tempeature annealing to be activated. In partly activated materials with the donor concentration in the 10(16) cm(-3) range or lower, the donor is found to behave as a negative-U center (often called a DX center) with the negative charge state DX- lying similar to 16-20 meV below the neutral charge state d(0) (or E-d), which is estimated to be similar to 28-29 meV below the conduction band minimum. This corresponds to a donor activation energy of E-a similar to 44-49 meV. In fully activated materials with the donor spin density close to similar to 1 x 10(18) cm(-3), donor electrons become delocalized, leading to the formation of impurity bands, which reduces the donor activation energy to E-a similar to 15-17 meV. The results clarify the electronic structure of the dominant donor in UID beta-Ga2O3 and explain the large variation in the previously reported donor activation energy. Published by AIP Publishing.

    DOI: 10.1063/1.4972040

  • Electron channel mobility in silicon-doped Ga2O3 MOSFETs with a resistive buffer layer Reviewed

    Man Hoi Wong, Kohei Sasaki, Akito Kuramata, Shigenobu Yamakoshi, Masataka Higashiwaki

    JAPANESE JOURNAL OF APPLIED PHYSICS   55 ( 12 )   2016.12( ISSN:0021-4922

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    The electron mobility in depletion-mode lateral beta-Ga2O3(010) metal-oxide-semiconductor field-effect transistors (MOSFETs) with an n-channel formed by Si-ion (Si+) implantation doping was extracted using low-field electrical measurements on FET structures. An undoped Ga2O3 buffer layer protected the channel against charge compensation by suppressing outdiffusion of deep Fe acceptors from the semi-insulating substrate. The molecular beam epitaxy growth temperature was identified as a key process parameter for eliminating parasitic conduction at the buffer/substrate growth interface. Devices with a resistive buffer showed room temperature channel mobilities of 90-100cm(2)V(-1) s(-1) at carrier concentrations of low-to mid-10(17)cm(-3), with small in-plane mobility anisotropy of 10-15% ascribable to anisotropic carrier scattering. (C) 2016 The Japan Society of Applied Physics

    DOI: 10.7567/JJAP.55.1202B9

  • Characterization of channel temperature in Ga2O3 metal-oxide-semiconductor field-effect transistors by electrical measurements and thermal modeling Reviewed

    Man Hoi Wong, Yoji Morikawa, Kohei Sasaki, Akito Kuramata, Shigenobu Yamakoshi, Masataka Higashiwaki

    APPLIED PHYSICS LETTERS   109 ( 19 )   2016.11( ISSN:0003-6951

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    The channel temperature (T-ch) and thermal resistance (R-th) of Ga2O3 metal-oxide-semiconductor field-effect transistors were investigated through electrical measurements complemented by electrothermal device simulations that incorporated experimental Ga2O3 thermal parameters. The analysis technique was based on a comparison between DC and pulsed drain currents (I-DS) at known applied biases, where negligible self-heating under pulsed conditions enabled approximation of T-ch to the ambient temperature (T-amb) and hence correlation of I-DS to T-ch. Validation of the device model was achieved through calibration against the DC data. The experimental T-ch was in good agreement with simulations for T-amb between 20 degrees C and 175 degrees C. A large R-th of 48 mm.K/W thus extracted at room temperature highlights the value of thermal analysis for understanding the degradation mechanisms and improving the reliability of Ga2O3 power devices. Published by AIP Publishing.

    DOI: 10.1063/1.4966999

  • Epitaxially grown crystalline Al

    Kamimura Takafumi, Krishnamurthy Daivasigamani, Kuramata Akito, Yamakoshi Shigenobu, Higashiwaki Masataka

    Jpn. J. Appl. Phys.   55 ( 12 )   1202B5   2016.10( ISSN:0021-4922

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    Al<inf>2</inf>O<inf>3</inf>films were deposited on β-Ga<inf>2</inf>O<inf>3</inf>(010) and β-Ga<inf>2</inf>O<inf>3</inf>[Formula: see text] substrates by atomic layer deposition at 250 °C, and their interface state densities (D<inf>it</inf>) at shallow energies were evaluated using a high–low capacitance–voltage (C–V) method. Al<inf>2</inf>O<inf>3</inf>/β-Ga<inf>2</inf>O<inf>3</inf>(010) showed lower D<inf>it</inf>values (5.9 × 10<sup>10</sup>to 9.3 × 10<sup>11</sup>cm<sup>−2</sup>eV<sup>−1</sup>) than Al<inf>2</inf>O<inf>3</inf>/β-Ga<inf>2</inf>O<inf>3</inf>[Formula: see text] (2.0 × 10<sup>11</sup>to 2.0 × 10<sup>12</sup>cm<sup>−2</sup>eV<sup>−1</sup>) in an energy range of −0.8 to −0.1 eV. Cross-sectional transmission electron microscopy analysis indicated the formation of a uniform amorphous Al<inf>2</inf>O<inf>3</inf>layer on the β-Ga<inf>2</inf>O<inf>3</inf>[Formula: see text] substrate. In contrast, a crystalline Al<inf>2</inf>O<inf>3</inf>interlayer with a thickness of 3.2 ± 0.7 nm with an amorphous Al<inf>2</inf>O<inf>3</inf>top layer was formed on the β-Ga<inf>2</inf>O<inf>3</inf>(010) substrate, which effectively decreased D<inf>it</inf>. Moreover, thicker interlayers showing lower D<inf>it</inf>values at deep state levels were formed at deposition temperatures higher than 100 °C, which were evaluated by shifts in the C–V curves.

    DOI: 10.7567/JJAP.55.1202B5

    CiNii Article

  • Theoretical and experimental investigation of optical absorption anisotropy in beta-Ga2O3 Reviewed

    F. Ricci, F. Boschi, A. Baraldi, A. Filippetti, M. Higashiwaki, A. Kuramata, V. Fiorentini, R. Fornari

    JOURNAL OF PHYSICS-CONDENSED MATTER   28 ( 22 )   2016.06( ISSN:0953-8984

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    The question of optical bandgap anisotropy in the monoclinic semiconductor beta-Ga2O3 was revisited by combining accurate optical absorption measurements with theoretical analysis, performed using different advanced computation methods. As expected, the bandgap edge of bulk beta-Ga2O3 was found to be a function of light polarization and crystal orientation, with the lowest onset occurring at polarization in the ac crystal plane around 4.5-4.6 eV; polarization along b unambiguously shifts the onset up by 0.2 eV. The theoretical analysis clearly indicates that the shift in the b onset is due to a suppression of the transition matrix elements of the three top valence bands at Gamma point.

    DOI: 10.1088/0953-8984/28/22/224005

  • Large conduction band offset at SiO2/-Ga2O3 heterojunction determined by X-ray photoelectron spectroscopy Reviewed

    Keita Konishi, Takafumi Kamimura, Man Hoi Wong, Kohei Sasaki, Akito Kuramata, Shigenobu Yamakoshi, Masataka Higashiwaki

    PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS   253 ( 4 )   623 - 625   2016.04( ISSN:0370-1972

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    We evaluated the band offsets at the SiO2/-Ga2O3 (010) interface by X-ray photoelectron spectroscopy (XPS). Plasma chemical vapor deposition with a liquid tetraethyl orthosilicate source for SiO2 was used to prepare an SiO2(40nm)/Ga2O3 sample and an SiO2(3nm)/Ga2O3 sample for XPS analyses. The bandgap of SiO2 was determined to be 8.7 +/- 0.2eV. A large conduction band offset of 3.1 +/- 0.2eV and a corresponding valence band offset of 1.0 +/- 0.2eV were determined for the SiO2/Ga2O3 interface. These results suggest that an SiO2 gate insulator is favorable for Ga2O3 field effect transistors operating under high temperatures.

    DOI: 10.1002/pssb.201552519

  • Recent progress in Ga2O3 power devices Reviewed

    Masataka Higashiwaki, Kohei Sasaki, Hisashi Murakami, Yoshinao Kumagai, Akinori Koukitu, Akito Kuramata, Takekazu Masui, Shigenobu Yamakoshi

    SEMICONDUCTOR SCIENCE AND TECHNOLOGY   31 ( 3 )   2016.03( ISSN:0268-1242

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    This is a review article on the current status and future prospects of the research and development on gallium oxide (Ga2O3) power devices. Ga2O3 possesses excellent material properties, in particular for power device applications. It is also attractive from an industrial viewpoint since large-size, high-quality wafers can be manufactured from a single-crystal bulk synthesized by melt-growth methods. These two features have drawn much attention to Ga2O3 as a new wide bandgap semiconductor following SiC and GaN. In this review, we describe the recent progress in the research and development on fundamental technologies of Ga2O3 devices, covering single-crystal bulk and wafer production, homoepitaxial thin film growth by molecular beam epitaxy and halide vapor phase epitaxy, as well as device processing and characterization of metal-semiconductor field-effect transistors, metal-oxide-semiconductor field-effect transistors and Schottky barrier diodes.

    DOI: 10.1088/0268-1242/31/3/034001

  • Temperature-dependent exciton resonance energies and their correlation with IR-active optical phonon modes in beta-Ga2O3 single crystals Reviewed

    T. Onuma, S. Saito, K. Sasaki, K. Goto, T. Masui, T. Yamaguchi, T. Honda, A. Kuramata, M. Higashiwaki

    APPLIED PHYSICS LETTERS   108 ( 10 )   2016.03( ISSN:0003-6951

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    Temperature-dependent exciton resonance energies E-exciton in beta-Ga2O3 single crystals are studied by using polarized reflectance measurement. The E-exciton values exhibit large energy changes in the range of 179-268 meV from 5 to 300 K. The IR-active A(u) and B-u optical phonon modes are selectively observed in the IR spectroscopic ellipsometry spectra by reflecting the polarization selection rules. The longitudinal optical (LO) phonon energies can be divided into three ranges: (h) over bar omega(LO) = 35-48, 70-73, and 88-99 meV. The broadening parameters, which are obtained from the reflectance measurements, correspond to the lower two ranges of (h) over bar omega(LO) at low temperature and 75 meV above 150 K. The large E-exciton changes with temperature in beta-Ga2O3 are found to be originated from the exciton-LO-phonon interaction. (C) 2016 AIP Publishing LLC.

    DOI: 10.1063/1.4943175

  • Anisotropy, phonon modes, and free charge carrier parameters in monoclinic beta-gallium oxide single crystals Reviewed

    M. Schubert, R. Korlacki, S. Knight, T. Hofmann, S. Schoeche, V. Darakchieva, E. Janzen, B. Monemar, D. Gogova, Q. -T. Thieu, R. Togashi, H. Murakami, Y. Kumagai, K. Goto, A. Kuramata, S. Yamakoshi, M. Higashiwaki

    PHYSICAL REVIEW B   93 ( 12 )   2016.03( ISSN:2469-9950

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    We derive a dielectric function tensor model approach to render the optical response of monoclinic and triclinic symmetry materials with multiple uncoupled infrared and far-infrared active modes. We apply our model approach to monoclinic beta-Ga2O3 single-crystal samples. Surfaces cut under different angles from a bulk crystal, (010) and ((2) over bar 01), are investigated by generalized spectroscopic ellipsometry within infrared and far-infrared spectral regions. We determine the frequency dependence of 4 independent beta-Ga2O3 Cartesian dielectric function tensor elements by matching large sets of experimental data using a point-by-point data inversion approach. From matching our monoclinic model to the obtained 4 dielectric function tensor components, we determine all infrared and far-infrared active transverse optic phonon modes with A(u) and B-u symmetry, and their eigenvectors within the monoclinic lattice. We find excellent agreement between our model results and results of density functional theory calculations. We derive and discuss the frequencies of longitudinal optical phonons in beta-Ga2O3. We derive and report density and anisotropic mobility parameters of the free charge carriers within the tin-doped crystals. We discuss the occurrence of longitudinal phonon plasmon coupled modes in beta-Ga2O3 and provide their frequencies and eigenvectors. We also discuss and present monoclinic dielectric constants for static electric fields and frequencies above the reststrahlen range, and we provide a generalization of the Lyddane-Sachs-Teller relation for monoclinic lattices with infrared and far-infrared active modes. We find that the generalized Lyddane-Sachs-Teller relation is fulfilled excellently for beta-Ga2O3.

    DOI: 10.1103/PhysRevB.93.125209

  • Temperature-dependent capacitance-voltage and current-voltage characteristics of Pt/Ga2O3 (001) Schottky barrier diodes fabricated on n(-)-Ga2O3 drift layers grown by halide vapor phase epitaxy Reviewed

    Masataka Higashiwaki, Keita Konishi, Kohei Sasaki, Ken Goto, Kazushiro Nomura, Quang Tu Thieu, Rie Togashi, Hisashi Murakami, Yoshinao Kumagai, Bo Monemar, Akinori Koukitu, Akito Kuramata, Shigenobu Yamakoshi

    APPLIED PHYSICS LETTERS   108 ( 13 )   2016.03( ISSN:0003-6951

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    We investigated the temperature-dependent electrical properties of Pt/Ga2O3 Schottky barrier diodes (SBDs) fabricated on n(-)-Ga2O3 drift layers grown on single-crystal n(+)-Ga2O3 (001) substrates by halide vapor phase epitaxy. In an operating temperature range from 21 degrees C to 200 degrees C, the Pt/Ga2O3 (001) Schottky contact exhibited a zero-bias barrier height of 1.09-1.15 eV with a constant near-unity ideality factor. The current-voltage characteristics of the SBDs were well-modeled by thermionic emission in the forward regime and thermionic field emission in the reverse regime over the entire temperature range. (C) 2016 AIP Publishing LLC.

    DOI: 10.1063/1.4945267

  • Field-Plated Ga2O3 MOSFETs With a Breakdown Voltage of Over 750 V Reviewed

    Man Hoi Wong, Kohei Sasaki, Akito Kuramata, Shigenobu Yamakoshi, Masataka Higashiwaki

    IEEE ELECTRON DEVICE LETTERS   37 ( 2 )   212 - 215   2016.02( ISSN:0741-3106

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    Publishing type:Research paper (scientific journal)  

    Depletion-mode field-plated Ga2O3 metal-oxide-semiconductor field-effect transistors were demonstrated for the first time. Substantial enhancement in breakdown voltage was achieved with a gate-connected field plate. The device channels, formed by selective-area Si ion implantation doping of an undoped Ga2O3 epilayer, were electrically isolated by the highly resistive epilayer without mesa etching. Effective surface passivation and high Ga2O3 material quality contributed to the absence of drain current collapse. The transistors exhibited an off-state breakdown voltage of 755 V, a high drain current on/off ratio of over 10(9), and stable high temperature operation against 300 degrees C thermal stress.

    DOI: 10.1109/LED.2015.2512279

  • Measurement of Channel Temperature in Ga2O3 MOSFETs Reviewed

    Man Hoi Wong, Yoji Morikawa, Kohei Sasaki, Akito Kuramata, Shigenobu Yamakoshi, Masataka Higashiwaki

    2016 COMPOUND SEMICONDUCTOR WEEK (CSW) INCLUDES 28TH INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE & RELATED MATERIALS (IPRM) & 43RD INTERNATIONAL SYMPOSIUM ON COMPOUND SEMICONDUCTORS (ISCS)   2016

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  • Ga2O3 Field-Plated Schottky Barrier Diodes with a Breakdown Voltage of Over 1 kV Reviewed

    Keita Konishi, Ken Goto, Quang Tu Thieu, Rie Togashi, Hisashi Murakami, Yoshinao Kumagai, Bo Monemar, Akito Kuramata, Shigenobu Yamakoshi, Masataka Higashiwaki

    2016 74TH ANNUAL DEVICE RESEARCH CONFERENCE (DRC)   2016

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  • Gallium oxide schottky barrier diodes Reviewed

    Masataka Higashiwaki, Kohei Sasaki, Hisashi Murakami, Yoshinao Kumagai, Akito Kuramata

    IEEJ Transactions on Electronics, Information and Systems   136 ( 4 )   479 - 483   2016( ISSN:1348-8155

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    The new wide-bandgap oxide semiconductor, gallium oxide (Ga2O3), has gained attraction as a promising candidate for power device applications because of its excellent material properties and suitability for mab production. Fundamental halide vapor phase epitaxy (HVPE) technology for Ga2O3thin film growth has been developed for development of vertical Ga2O3devices. Unintentionally-doped Ga2O3layers grown by HVPE were high purity and high crystalline quality, and an electron density in the Ga2O3film can be precisely controlled by Si doping in the wide range of n=1015- 1018 cm-3. We fabricated vertical Ga2O3Schottky barrier diodes (SBDs) with HVPE-grown n-Ga2O3drift layers on single-crystal β-Ga2O3(001) substrates. The SBDs demonstrated promising device performance as next-generation power devices, such as the specific on-resistances of about 3.0 mωcm2, the ideality factors of almost equal to unity, and the off-state breakdown voltage of about -500 V.

    DOI: 10.1541/ieejeiss.136.479

  • Valence band ordering in beta-Ga2O3 studied by polarized transmittance and reflectance spectroscopy Reviewed

    Takeyoshi Onuma, Shingo Saito, Kohei Sasaki, Tatekazu Masui, Tomohiro Yamaguchi, Tohru Honda, Masataka Higashiwaki

    JAPANESE JOURNAL OF APPLIED PHYSICS   54 ( 11 )   2015.11( ISSN:0021-4922

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    The polarized transmittance and reflectance spectra of beta-Ga2O3 crystals are investigated, and the data are interpreted in terms of the monoclinic crystal band structure. The energies of the absorption edge can be divided into six ranges, and these ranges can be assigned to the transitions from the valence bands to the conduction band minimum according to the selection rules. The indirect bandgap-energy of 4.43 eV is smaller than the direct bandgap-energy of 4.48 eV at RT; and the energy difference of 0.05 eV nearly matches the theoretically calculated values of 0.03-0.04 eV. (C) 2015 The Japan Society of Applied Physics

    DOI: 10.7567/JJAP.54.112601

  • Impacts of AlOx formation on emission properties of AlN/GaN heterostructures Reviewed

    Takeyoshi Onuma, Yohei Sugiura, Tomohiro Yamaguchi, Tohru Honda, Masataka Higashiwaki

    APPLIED PHYSICS EXPRESS   8 ( 5 )   1 - 52401   2015.05( ISSN:1882-0778

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    The effects of AlOx formation on the emission properties of AlN/GaN heterostructures are comparatively investigated using steady-state and time-resolved photoluminescence (PL) measurements. By analyzing the excitation power and temperature-dependent PL spectra, PL at around 3.45-3.46 eV is attributed to the two-dimensional electron-gas (2DEG)-related emission. Simultaneous changes in the emission energies and lifetimes are observed by forming a crystallized AlOx layer. The results demonstrate a possibility of controlling the surface states by changing the surface oxide structure. (C) 2015 The Japan Society of Applied Physics

    DOI: 10.7567/APEX.8.052401

    J-GLOBAL

  • Anisotropic thermal conductivity in single crystal beta-gallium oxide Reviewed

    Zhi Guo, Amit Verma, Xufei Wu, Fangyuan Sun, Austin Hickman, Takekazu Masui, Akito Kuramata, Masataka Higashiwaki, Debdeep Jena, Tengfei Luo

    APPLIED PHYSICS LETTERS   106 ( 11 )   111909-1 - 111909-5   2015.03( ISSN:0003-6951

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    The thermal conductivities of beta-Ga2O3 single crystals along four different crystal directions were measured in the temperature range of 80-495K using the time domain thermoreflectance method. A large anisotropy was found. At room temperature, the [010] direction has the highest thermal conductivity of 27.0 +/- 2.0 W/mK, while that along the [100] direction has the lowest value of 10.9 +/- 1.0 W/mK. At high temperatures, the thermal conductivity follows a similar to 1/T relationship characteristic of Umklapp phonon scattering, indicating phonon-dominated heat transport in the beta-Ga2O3 crystal. The measured experimental thermal conductivity is supported by first-principles calculations, which suggest that the anisotropy in thermal conductivity is due to the differences of the speed of sound along different crystal directions. (C) 2015 AIP Publishing LLC.

    DOI: 10.1063/1.4916078

  • Anomalous Fe diffusion in Si-ion-implanted beta-Ga2O3 and its suppression in Ga2O3 transistor structures through highly resistive buffer layers Reviewed

    Man Hoi Wong, Kohei Sasaki, Akito Kuramata, Shigenobu Yamakoshi, Masataka Higashiwaki

    APPLIED PHYSICS LETTERS   106 ( 3 )   2015.01( ISSN:0003-6951

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    The thermal behavior of Fe as a compensating acceptor impurity in beta-Ga2O3 (010) was studied in view of growing interests in semi-insulating Fe-doped Ga2O3 substrates for the realization of high-performance Ga2O3 field-effect transistors (FETs). An anomalous redistribution of Fe beyond the extent of intrinsic thermal diffusion was revealed by secondary ion mass spectroscopy in device-relevant structures where Ga2O3 grown homoepitaxially on Fe-doped substrates was doped by Si ion (Si+) implantation and annealed at high temperatures. The enhanced Fe diffusion was attributed to an athermal process involving intrinsic defects from the region of implantation damage. An undoped Ga2O3 buffer between the Si+-implanted layer and the Fe-doped substrate effectively suppressed Fe outdiffusion by protecting the substrate against unintentional ion damage or defects from a remote source, thereby preserving the electrical integrity of the Si-doped material. Temperature-dependent current-voltage measurements indicated that the undoped Ga2O3 buffer was highly resistive with inter-device leakage attributable to surface conduction via a variable-range hopping mechanism. The buffer scheme, together with dielectric passivation to eliminate surface leakage, was proposed to constitute an integral process module for future lateral Ga2O3 FET devices. (C) 2015 AIP Publishing LLC.

    DOI: 10.1063/1.4906375

    J-GLOBAL

  • Homoepitaxial growth of beta-Ga2O3 layers by halide vapor phase epitaxy Reviewed

    Hisashi Murakami, Kazushiro Nomura, Ken Goto, Kohei Sasaki, Katsuaki Kawara, Quang Tu Thieu, Rie Togashi, Yoshinao Kumagai, Masataka Higashiwaki, Akito Kuramata, Shigenobu Yamakoshi, Bo Monemar, Akinori Koukitu

    Applied Physics Express   8 ( 1 )   2015.01( ISSN:1882-0778

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    Thick high-purity beta-Ga2O3 layers of high crystalline quality were grown homoepitaxially by halide vapor phase epitaxy (HVPE) using gaseous GaCl and O-2 on (001) beta-Ga2O3 substrates prepared by edge-defined film-fed growth. The surface morphology and structural quality of the grown layer improved with increasing growth temperature. X-ray diffraction omega-rocking curves for the (002) and (400) reflections for the layer grown at 1000 degrees C had small full widths at half maximum. Secondary ion mass spectrometry and electrical characteristics revealed that the growth of high-purity beta-Ga2O3 layers with low effective donor concentration (N-d - N-a &lt; 10(13) cm(-3)) is possible by HVPE. (C) 2015 The Japan Society of Applied Physics

    DOI: 10.7567/APEX.8.015503

    J-GLOBAL

  • Current Status of Gallium Oxide-Based Power Device Technology Reviewed

    Masataka Higashiwaki, Kohei Sasaki, Man Hoi Wong, Takafumi Kamimura, Ken Goto, Kazushiro Nomura, Quang Tu Thieu, Rie Togashi, Hisashi Murakami, Yoshinao Kumagai, Bo Monemar, Akinori Koukitu, Akito Kuramata, Takekazu Masui, Shigenobu Yamakoshi

    2015 IEEE COMPOUND SEMICONDUCTOR INTEGRATED CIRCUIT SYMPOSIUM (CSICS)   2015( ISSN:2162-7940

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    Publishing type:Research paper (international conference proceedings)  

    Gallium oxide (Ga2O3) possesses excellent material properties especially for power device applications. It is also attractive from an industrial viewpoint since large -size, high quality wafers can be manufactured by using simple methods. These two features have drawn much attention to Ga2O3 as a new wide bandgap semiconductor following SiC and GaN. In this report, we describe the recent progress in development on fundamental technologies for Ga2O3 devices, covering wafer production from melt -grown bulk single crystals, homoepitaxial thin-film growth by halide vapor phase epitaxy, as well as device processing and characterization of metal -oxide -semiconductor field-effect transistors and Schottky barrier diodes.

    DOI: 10.1109/CSICS.2015.7314495

  • Ga2O3 Schottky Barrier Diodes with n(-)-Ga2O3 Drift Layers Grown by HVPE Reviewed

    Masataka Higashiwaki, Kohei Sasaki, Ken Goto, Kazushiro Nomura, Quang Tu Thieu, Rie Togashi, Hisashi Murakami, Yoshinao Kumagai, Bo Monemar, Akinori Koukitu, Akito Kuramata, Shigenobu Yamakoshi

    2015 73RD ANNUAL DEVICE RESEARCH CONFERENCE (DRC)   29 - 30   2015

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  • Estimation of Carrier Density of Wide Bandgap Semiconductor beta-Ga2O3 Single Crystals by THz Reflectance Measurement Reviewed

    Shingo Saito, Takeyoshi Onuma, Kohei Sasaki, Akito Kuramata, Norihiko Sekine, Akifumi Kasamatsu, Masataka Higashiwaki

    2015 40TH INTERNATIONAL CONFERENCE ON INFRARED, MILLIMETER AND TERAHERTZ WAVES (IRMMW-THZ)   2015( ISSN:2162-2027

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    Publishing type:Research paper (international conference proceedings)  

    In order to estimate carrier density on wide bandgap semiconductor beta-Ga2O3, we made a measurement of THz reflectance spectra of beta-Ga2O3 samples by using a THz time-domain spectroscopic method. The tails of reflectance structures were shifted to higher energy side with increasing the carrier density. We treated the structure was caused by plasmon, and calculated the carrier density of each samples. The carrier densities obtained by the THz reflection measurements showed a good agreement with the results by Hall-effect measurements. These results indicated that THz spectroscopy is a useful method to estimate the carrier density of beta-Ga2O3 samples.

  • Growth of crystallized AlOx on AlN/GaN heterostructures by in-situ RF-MBE Reviewed

    Yohei Sugiura, Tohru Honda, Masataka Higashiwaki

    JOURNAL OF CRYSTAL GROWTH   405   64 - 67   2014.11( ISSN:0022-0248

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    Publishing type:Research paper (scientific journal)  

    We report successful growth of a crystallized AlOx layer on top of AlN/GaN heterostructures by using RF-plasma molecular-beam epitaxy for exploring a new-type oxide/nitride heterostructure system. The insertion of an AlOx, buffer layer, which was formed by following three steps of (i) an Al metal deposition at 150 degrees C, (ii) an oxidation of the Al metal by oxygen plasma irradiation, and (iii) an annealing of the oxidized layer at 800 degrees C, facilitated the formation of a crystalline AlOx, layer on top of the AlN/GaN structures. Surface morphologies observed by atomic force microscope showed that the AlOx, buffer layer was directly formed on the nitride structure and fully covered the AlN layer. The AlOx, top layer grown on the buffer layer had a flat and smooth surface. A cross-sectional transmission electron microscopy micrograph revealed that the AlOx thin film grown at 800 degrees C on the nitride structure was fully crystallized. (C) 2014 Elsevier B.V. All rights reservecl.

    DOI: 10.1016/j.jcrysgro.2014.07.055

    J-GLOBAL

  • Systematic investigation of the growth rate of beta-Ga2O3(010) by plasma-assisted molecular beam epitaxy Reviewed

    Hironori Okumura, Masao Kita, Kohei Sasaki, Akito Kuramata, Masataka Higashiwaki, James S. Speck

    APPLIED PHYSICS EXPRESS   7 ( 9 )   1 - 95501   2014.09( ISSN:1882-0778

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    beta-Ga2O3(010) homo-epitaxial growth was performed by plasma-assisted molecular beam epitaxy. Under Ga-rich conditions and for growth temperatures above 650 degrees C, the growth rate was independent of the Ga/O ratio (&gt;1). A high growth rate of 2.2 nm/min for beta-Ga2O3(010) was achieved by optimizing the O flux between 650 and 750 degrees C. Under Ga-rich conditions between growth temperatures of 500-900 degrees C, smooth surfaces with rms roughness below 1 nm were realized. We found that the slightly Ga-rich conditions between 650 and 750 degrees C were optimal for beta-Ga2O3(010) growth with a smooth surface and a high growth rate. (C) 2014 The Japan Society of Applied Physics

    DOI: 10.7567/APEX.7.095501

    J-GLOBAL

  • Polarized Raman spectra in beta-Ga2O3 single crystals Reviewed

    T. Onuma, S. Fujioka, T. Yamaguchi, Y. Itoh, M. Higashiwaki, K. Sasaki, T. Masui, T. Honda

    JOURNAL OF CRYSTAL GROWTH   401   330 - 333   2014.09( ISSN:0022-0248

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    Polarized Raman spectra were measured from (010) Mg-doped, (100) Si-doped, and (001) unintentionally doped beta-Ga2O3 substrates prepared by either the floating zone growth or edge-defined film-fed growth methods. The A(g) and B-g Raman active modes were perfectly separated in the spectra according to the polarization selection rules. To the best of our knowledge, this is the first experimental observation of a complete set of polarized Raman spectra of beta-Ga2O3. The results are ensured by the high uniformity of crystalline orientation and surface flatness of the present substrates. (C) 2014 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.jcrysgro.2013.12.061

  • Band alignment and electrical properties of Al2O3/beta-Ga2O3 heterojunctions Reviewed

    Takafumi Kamimura, Kohei Sasaki, Man Hoi Wong, Daivasigamani Krishnamurthy, Akito Kuramata, Takekazu Masui, Shigenobu Yamakoshi, Masataka Higashiwaki

    APPLIED PHYSICS LETTERS   104 ( 19 )   2014.05( ISSN:0003-6951

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    The band alignment of Al2O3/n-Ga2O3 was investigated by x-ray photoelectron spectroscopy (XPS). With a band gap of 6.8+/-0.2 eV measured for Al2O3, the conduction and valence band offsets at the interface were estimated to be 1.5+/-0.2 eV and 0.7+/-0.2 eV, respectively. The conduction band offset was also obtained from tunneling current in Al2O3/n-Ga2O3 ((2) over bar 01) metal-oxide-semiconductor (MOS) diodes using the Fowler-Nordheim model. The electrically extracted value was in good agreement with the XPS data. Furthermore, the MOS diodes exhibited small capacitance-voltage hysteresis loops, indicating the successful engineering of a high-quality Al2O3/Ga2O3 interface. (C) 2014 AIP Publishing LLC.

    DOI: 10.1063/1.4876920

    J-GLOBAL

  • Growth temperature dependences of structural and electrical properties of Ga2O3 epitaxial films grown on beta-Ga2O3 (010) substrates by molecular beam epitaxy Reviewed

    Kohei Sasaki, Masataka Higashiwaki, Akito Kuramata, Takekazu Masui, Shigenobu Yamakoshi

    JOURNAL OF CRYSTAL GROWTH   392   30 - 33   2014.04( ISSN:0022-0248

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    We investigated the growth temperature dependence of the structural and electrical properties of Sn-doped Ca2O3 homoepitaxial films grown on single crystal beta-Ga2O3 (010) substrates by molecular beam epitaxy. Ca2O3 films with an atomically smooth surface were obtained at growth temperatures of 550-650 degrees C. On the other hand, a delay in the incorporation of Sn atoms in Ca2O3, which was probably due to segregation, occurred in the initial stage of growth at higher than 600 degrees C. To ensure that Sn-doped Ca2O3 films with both high crystal quality and accurately controlled carrier density are obtained, the optimum growth temperature should be set at 540-570 degrees C. (c) 2014 Elsevier EN. All rights reserved

    DOI: 10.1016/j.jcrysgro.2014.02.002

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  • Development of gallium oxide power devices Invited Reviewed

    Masataka Higashiwaki, Kohei Sasaki, Akito Kuramata, Takekazu Masui, Shigenobu Yamakoshi

    PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE   211 ( 1 )   21 - 26   2014.01( ISSN:1862-6300

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    Gallium oxide (Ga2O3) is a strong contender for power electronic devices. The material possesses excellent properties such as a large bandgap of 4.7-4.9eV for a high breakdown field of 8MVcm(-1). Low cost, high volume production of large single-crystal -Ga2O3 substrates can be realized by melt-growth methods commonly adopted in the industry. High-quality n-type Ga2O3 epitaxial thin films with controllable carrier densities were obtained by ozone molecular beam epitaxy (MBE). We fabricated Ga2O3 metal-semiconductor field-effect transistors (MESFETs) and Schottky barrier diodes (SBDs) from single-crystal Ga2O3 substrates and MBE-grown epitaxial wafers. The MESFETs delivered excellent device performance including an off-state breakdown voltage (V-br) of over 250V, a low leakage current of only few Amm(-1), and a high drain current on/off ratio of about four orders of magnitude. The SBDs also showed good characteristics such as near-unity ideality factors and high reverse V-br. These results indicate that Ga2O3 can potentially meet or even exceed the performance of Si and typical widegap semiconductors such as SiC or GaN for ultrahigh-voltage power switching applications. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

    DOI: 10.1002/pssa.201330197

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  • Crystal Growth and Device Application of Gallium Oxide (Ga<sub>2</sub>O<sub>3</sub>)

    HIGASHIWAKI Masataka, SASAKI Kohei

    J. Surf. Sci. Soc. Jpn.   35 ( 2 )   102 - 107   2014( ISSN:0388-5321

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    Gallium oxide (Ga<sub>2</sub>O<sub>3</sub>) has excellent material properties for power device applications represented by the extremely large breakdown field due to a large bandgap of 4.7-4.9 eV. Another important feature in industry is that large single-crystal <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> bulks and wafers can be fabricated with melt-growth methods. We recently succeeded in fabricating Ga<sub>2</sub>O<sub>3</sub> metal-oxide-semiconductor field-effect transistors (MOSFETs) by using newly developed technologies for making single-crystal bulks, growing conductivity-controlled epitaxial films, and fabricating devices. The MOSFETs exhibited excellent device characteristics including an off-state breakdown voltage over 370 V, an extremely low leakage current, and a high on/off drain current ratio of more than ten orders of magnitude. These results indicate that Ga<sub>2</sub>O<sub>3</sub> have comparable or even more potential than Si and typical widegap semiconductors SiC and GaN for power device applications.

    DOI: 10.1380/jsssj.35.102

    CiNii Article

    Other URL: https://jlc.jst.go.jp/DN/JALC/10028793754?from=CiNii

  • Current status and future prospect of R &amp; D on gallium oxide power devices

    Higashiwaki, M.

    Journal of the Institute of Electronics, Information and Communication Engineers   97 ( 3 )   2014

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  • Depletion-mode Ga2O3 metal-oxide-semiconductor field-effect transistors on β-Ga2O3 (010) substrates and temperature dependence of their device characteristics Reviewed

    Masataka Higashiwaki, Kohei Sasaki, Takafumi Kamimura, Man Hoi Wong, Daivasigamani Krishnamurthy, Akito Kuramata, Takekazu Masui, Shigenobu Yamakoshi

    Applied Physics Letters   103 ( 12 )   2013.09( ISSN:0003-6951

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    Single-crystal gallium oxide (Ga2O3) metal-oxide-semiconductor field-effect transistors were fabricated on a semi-insulating β-Ga2O3 (010) substrate. A Sn-doped n-Ga2O3 channel layer was grown by molecular-beam epitaxy. Si-ion implantation doping was performed to source and drain electrode regions for obtaining low-resistance ohmic contacts. An Al2O3 gate dielectric film formed by atomic layer deposition passivated the device surface and significantly reduced gate leakage. The device with a gate length of 2 μm showed effective gate modulation of the drain current with an extremely low off-state drain leakage of less than a few pA/mm, leading to a high drain current on/off ratio of over ten orders of magnitude. A three-terminal off-state breakdown voltage of 370 V was achieved. Stable transistor operation was sustained at temperatures up to 250 ° C. © 2013 AIP Publishing LLC.

    DOI: 10.1063/1.4821858

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  • Si-Ion Implantation Doping in beta-Ga2O3 and Its Application to Fabrication of Low-Resistance Ohmic Contacts Reviewed

    Kohei Sasaki, Masataka Higashiwaki, Akito Kuramata, Takekazu Masui, Shigenobu Yamakoshi

    APPLIED PHYSICS EXPRESS   6 ( 8 )   1 - 86502   2013.08( ISSN:1882-0778

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    We developed a donor doping technique for beta-Ga2O3 by using Si-ion (Si+) implantation. For the implanted Ga2O3 substrates with Si+ = 1 x 10(19) -5 x 10(19) cm(-3), a high activation efficiency of above 60% was obtained after annealing in a nitrogen gas atmosphere at a relatively low temperature of 900-1000 degrees C. Annealed Ti/Au electrodes fabricated on the implanted Ga2O3 layers showed ohmic behavior. The Ga2O3 with Si+ = 5 x 10(19) cm(-3) showed the lowest specific contact resistance and resistivity obtained in this work of 4.6 x 10(-6) Omega.cm(2) and 1.4m Omega.cm, respectively. (C) 2013 The Japan Society of Applied Physics

    DOI: 10.7567/APEX.6.086502

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  • Correlation between blue luminescence intensity and resistivity in beta-Ga2O3 single crystals Reviewed

    T. Onuma, S. Fujioka, T. Yamaguchi, M. Higashiwaki, K. Sasaki, T. Masui, T. Honda

    APPLIED PHYSICS LETTERS   103 ( 4 )   041910   2013.07( ISSN:0003-6951

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    Temperature-dependent cathodoluminescence spectra were measured from (001) unintentionally doped, (100) Si-doped, and (010) Mg-doped beta-Ga2O3 substrates prepared by either the floating zone growth or edge-defined film-fed growth methods. Although beta-Ga2O3 is expected to be an indirect bandgap material, direct Gamma-Gamma transitions were found to be dominant in the optical transmittance spectra. The substrates exhibited no near-band-edge emission and instead exhibited ultraviolet luminescence, blue luminescence (BL), and green luminescence bands. Since the BL intensity strongly depended on the resistivity in the crystals, there was evidence of a correlation between the BL intensity and formation energy of oxygen vacancies. (C) 2013 AIP Publishing LLC.

    DOI: 10.1063/1.4816759

  • Ga2O3 Schottky Barrier Diodes Fabricated by Using Single-Crystal beta-Ga2O3 (010) Substrates Reviewed

    Kohei Sasaki, Masataka Higashiwaki, Akito Kuramata, Takekazu Masui, Shigenobu Yamakoshi

    IEEE ELECTRON DEVICE LETTERS   34 ( 4 )   493 - 495   2013.04( ISSN:0741-3106

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    We fabricated gallium oxide (Ga2O3) Schottky barrier diodes using beta-Ga2O3 single-crystal substrates produced by the floating-zone method. The crystal quality of the substrates was excellent; the X-ray diffraction rocking curve peak had a full width at half-maximum of 32 arcsec, and the etch pit density was less than 1 x 10(4) cm(-2). The devices exhibited good characteristics, such as an ideality factor close to unity and a reasonably high reverse breakdown voltage of about 150 V. The Schottky barrier height of the Pt/beta-Ga2O3 interface was estimated to be 1.3-1.5 eV.

    DOI: 10.1109/LED.2013.2244057

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  • Research and development on Ga2O3 transistors and diodes Reviewed

    Masataka Higashiwaki, Kohei Sasaki, Man Hoi Wong, Takafumi Kamimura, Daivasigamani Krishnamurthy, Akito Kuramata, Takekazu Masui, Shigenobu Yamakoshi

    2013 1ST IEEE WORKSHOP ON WIDE BANDGAP POWER DEVICES AND APPLICATIONS (WIPDA)   100 - 103   2013

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    New widegap compound semiconductor gallium oxide (Ga2O3) power devices have been attracted as strong candidates for future power electronics. Here, we will introduce material properties, productivity of Ga2O3, and current status of research and development on its transistors and diodes.

  • MBE grown Ga2O3 and its power device applications Reviewed

    Kohei Sasaki, Masataka Higashiwaki, Akito Kuramata, Takekazu Masui, Shigenobu Yamakoshi

    Journal of Crystal Growth   378   591 - 595   2013( ISSN:0022-0248

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    N-type gallium oxide (Ga2O3) homoepitaxial thick films were grown on β-Ga2O3 (010) substrates by molecular beam epitaxy. The epitaxial growth rate was increased by more than 10 times by changing from the (100) plane to the (010) plane. The carrier concentration of the epitaxial layers could be varied within the range of 1016-1019 cm-3 by changing the Sn doping concentration. Schottky barrier diodes (SBDs) and metal-semiconductor field-effect transistors (MESFETs) on β-Ga2O3 homoepitaxial layers were demonstrated for the first time. The SBDs exhibited good device characteristics such as an ideality factor of 1.13, and high breakdown voltage about 125 V. The MESFETs also exhibited excellent characteristics such as a perfect pinch-off of the drain current, off-state breakdown voltage over 250 V, high on/off drain current ratio of around 10 4, and small gate leakage current. These device characteristics clearly indicate the great potential of Ga2O3 as a high-power device material. © 2013 Elsevier B.V All rights reserved.

    DOI: 10.1016/j.jcrysgro.2013.02.015

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  • Depletion-Mode Ga2O3 MOSFETs on beta-Ga2O3 (010) Substrates with Si-Ion-Implanted Channel and Contacts Reviewed

    Masataka Higashiwaki, Kohei Sasaki, Man Hoi Wong, Takafumi Kamimura, Daivasigamani Krishnamurthy, Akito Kuramata, Takekazu Masui, Shigenobu Yamakoshi

    2013 IEEE INTERNATIONAL ELECTRON DEVICES MEETING (IEDM)   2013

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    Depletion-mode Ga2O3 MOSFETs were fabricated on single-crystal beta-Ga2O3 (010) substrates. We applied Si-ion implantation to the ohmic contacts for low contact resistance as well as to the channel layer for reliable doping. An Al2O3 gate dielectric film formed by atomic layer deposition passivated the device surface and significantly reduced gate leakage. The MOSFETs with a simple structure exhibited complete channel pinch-off with a breakdown voltage of 415 V and a drain current on/off ratio of ten orders of magnitude at room temperature. The devices also showed stable operation up to 250 degrees C.

    DOI: 10.1109/IEDM.2013.6724713

  • Depletion-mode Ga2O3 MOSFETs Reviewed

    Masataka Higashiwaki, Kohei Sasaki, Takafumi Kamimura, Man Hoi Wong, Daivasigamani Krishnamurthy, Akito Kuramata, Takekazu Masui, Shigenobu Yamakoshi

    2013 71ST ANNUAL DEVICE RESEARCH CONFERENCE (DRC)   2013( ISSN:1548-3770

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  • Gallium oxide (Ga2O3) metal-semiconductor field-effect transistors on single-crystal beta-Ga2O3 (010) substrates Reviewed

    Masataka Higashiwaki, Kohei Sasaki, Akito Kuramata, Takekazu Masui, Shigenobu Yamakoshi

    APPLIED PHYSICS LETTERS   100 ( 1 )   13504   2012.01( ISSN:0003-6951

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    We report a demonstration of single-crystal gallium oxide (Ga2O3) metal-semiconductor field-effect transistors (MESFETs). A Sn-doped Ga2O3 layer was grown on a semi-insulating beta-Ga2O3 (010) substrate by molecular-beam epitaxy. We fabricated a circular MESFET with a gate length of 4 mu m and a source-drain spacing of 20 mu m. The device showed an ideal transistor action represented by the drain current modulation due to the gate voltage (V-GS) swing. A complete drain current pinch-off characteristic was also obtained for VGS &lt; -20 V, and the three-terminal off-state breakdown voltage was over 250 V. A low drain leakage current of 3 mu A at the off-state led to a high on/off drain current ratio of about 10000. These device characteristics obtained at the early stage indicate the great potential of Ga2O3-based electrical devices for future power device applications. (C) 2012 American Institute of Physics. [doi:10.1063/1.3674287]

    DOI: 10.1063/1.3674287

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  • Ga2O3 Schottky barrier diodes fabricated on single-crystal β-Ga2O3 substrates Reviewed

    Kohei Sasaki, Masataka Higashiwaki, Akito Kuramata, Takekazu Masui, Shigenobu Yamakoshi

    Device Research Conference - Conference Digest, DRC   159 - 160   2012( ISSN:1548-3770

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    β-Ga2O3 has an extremely large bandgap of 4.8-4.9 eV and excellent material properties for power device applications, as summarized in Tab. 1. The breakdown field of β-Ga2O3 is estimated to be 8 MV/cm, from the relation between the band gaps and breakdown fields of other major semiconductors. Another important feature is that large single-crystal β-Ga2O3 substrates can be fabricated with melt-growth methods such as floating-zone (FZ) and edge-defined film-fed growth (EFG). Figure 1 shows a photograph of a 2-inch-diameter single-crystal β-Ga2O3 wafer fabricated by the EFG method. The wafer size depends on the production machine size. Therefore, we consider that Ga2O3 is a very attractive new semiconductor for power device applications because of its material properties and ease of mass production. However, it has not been studied to any extent up to now. © 2012 IEEE.

    DOI: 10.1109/DRC.2012.6257021

  • Two-Stage High-Gain High-Power Distributed Amplifier Using Dual-Gate GaN HEMTs Reviewed

    Rajkumar Santhakumar, Brian Thibeault, Masataka Higashiwaki, Stacia Keller, Zhen Chen, Umesh K. Mishra, Robert A. York

    IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES   59 ( 8 )   2059 - 2063   2011.08( ISSN:0018-9480

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    A two-stage distributed amplifier monolithic microwave integrated circuit (MMIC) has been designed and fabricated using dual-gate GaN HEMTs. The measured small-signal gain of the MMIC is about 20 dB over the frequency range of 2-18 GHz. Measured peak saturated output power is about 2 W. A low interstage impedance of 25 is chosen for two reasons. It leads to larger size of the HEMTs in the output stage, and hence, increases output power without reducing the bandwidth. It also keeps the inter-stage transmission lines short, and hence, results in a very compact two-stage design with high gain. To enhance the output power further, capacitive division technique is used in the second stage. Dual-gate HEMTs are used, as they are compact and provide superior performance when compared to standard HEMTs.

    DOI: 10.1109/TMTT.2011.2144996

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  • Effects of Barrier Thinning on Small-Signal and 30-GHz Power Characteristics of AlGaN/GaN Heterostructure Field-Effect Transistors Reviewed

    Masataka Higashiwaki, Yi Pei, Rongming Chu, Umesh K. Mishra

    IEEE TRANSACTIONS ON ELECTRON DEVICES   58 ( 6 )   1681 - 1686   2011.06( ISSN:0018-9383

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    Short-gate AlGaN/GaN heterostructure field-effect transistors (HFETs) with extremely thin AlGaN barrier layers were fabricated and characterized from the viewpoint of millimeter-wave applications. The devices showed good direct-current and small-signal characteristics; however, the 30-GHz power characteristics were degraded due to frequency dispersion caused by the SiN(x)/AlGaN interface states. The dispersive behavior of the thin barrier devices measured in pulse I-V curves was different from the commonly observed one for the devices with normal AlGaN barrier thicknesses of 20-30 nm. The first characteristic point was that it happened only for structures with extremely thin barrier layers. As another unique point, the drain current collapse in the pulsed modes was observed only at a positive gate bias. We consider that the unique dispersion of the thin barrier HFETs was caused by the different charging paths related to hot electrons accelerated in a high electric field region of a 2-D electron gas (2DEG) channel. It seems reasonable to suppose that, for the extremely thin barrier structures, the AlGaN surface states can be charged not only by injected electrons from the gate metal through the SiN(x)/AlGaN interface but also by the hot electrons overcoming the barrier from the 2DEG formed at the AlGaN/GaN interface.

    DOI: 10.1109/TED.2011.2131653

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  • Distributed surface donor states and the two-dimensional electron gas at AlGaN/GaN heterojunctions Reviewed

    Luke Gordon, Mao-Sheng Miao, Srabanti Chowdhury, Masataka Higashiwaki, Umesh K. Mishra, Chris G. Van de Walle

    JOURNAL OF PHYSICS D-APPLIED PHYSICS   43 ( 50 )   1 - 8   2010.12( ISSN:0022-3727

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    Surface donor states with distributed and finite density are implemented in Schrodinger-Poisson simulations of AlGaN/GaN high electron mobility transistors, with the goal of studying their effects on the two-dimensional electron gas. Our recent experimental observations of an increasing surface barrier height with increasing AlGaN thickness are fitted very well by simulations including surface donor levels represented by a constant density of states (DOS) with a density on the order of 10(13) cm(-2) eV(-1). The highest occupied surface states are found to be around 1 eV below the conduction-band minimum, considerably higher in energy than previously reported single surface donor levels. These trends can be explained by the features of oxidized AlGaN surfaces. Furthermore, the surface DOS that fit the experimental results are found to be larger for samples with higher Al concentration.

    DOI: 10.1088/0022-3727/43/50/505501

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  • Effects of oxidation on surface chemical states and barrier height of AlGaN/GaN heterostructures Reviewed

    Masataka Higashiwaki, Srabanti Chowdhury, Brian L. Swenson, Umesh K. Mishra

    APPLIED PHYSICS LETTERS   97 ( 22 )   222104   2010.11( ISSN:0003-6951

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    The effects of oxidation on the surface structure and chemical bonding states of AlGaN/GaN heterostructures were investigated using x-ray photoelectron spectroscopy (XPS). In comparing Al 2p core-level XPS spectra among as-grown and annealed samples, we found that Al atoms on the surface were highly oxidized after rapid thermal annealing (RTA) at high temperature; not only in an O(2) but also in an N(2) gas atmosphere. The Al oxidation level was almost identical for the samples annealed at 800 degrees C, irrespective of the annealing atmosphere and time; yet there was a strong dependence on the annealing temperature. The dependence of surface barrier height on the annealing condition is associated with Al oxidation behavior. Before the RTA, the barrier height increased together with the AlGaN thickness, indicating an unpinned Fermi level and the existence of low-density and distributed surface donor states. After the high-temperature RTA, however, the height is maintained at a certain value, regardless of the thickness, due to Fermi level pinning by high-density donor states. These results can be explained by the formation of two types of oxide structures providing different types of donor states. (C) 2010 American Institute of Physics. [doi:10.1063/1.3522649]

    DOI: 10.1063/1.3522649

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  • Distribution of donor states on etched surface of AlGaN/GaN heterostructures Reviewed

    Masataka Higashiwaki, Srabanti Chowdhury, Mao-Sheng Miao, Brian L. Swenson, Chris G. Van de Walle, Umesh K. Mishra

    JOURNAL OF APPLIED PHYSICS   108 ( 6 )   63719   2010.09( ISSN:0021-8979

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    The dependence of electron density (n(s)) on AlGaN barrier thickness (d(AlGaN)) was studied for AlGaN/GaN single heterostructures whose d(AlGaN) was controlled by low-power Cl-based reactive ion etching (RIE) instead of growth. The samples showed a constant increase not only in n(s) but also in AlGaN surface barrier height (e phi(B)) with d(AlGaN), indicating the existence of low-density and distributed donor states on the AlGaN surface. Such a distribution of donor states differs from the commonly accepted model based on high-density and single-level surface donor states as the source of electrons in the two-dimensional electron gas (2DEG). The presence of a distribution of donor states is confirmed by first-principles calculations for a variety of surface structures for oxidized AlGaN surfaces. Donor states arise from areas of the surface that deviate from the electron-counting rule, leading to occupied surface states in the upper half of the band gap. The oxide formed on the surface after RIE results in a low-density distribution of surface donor states in which the highest occupied levels span the range from 1-2 eV below the AlGaN conduction-band minimum. The density of these states is comparable to the n(s) in the 2DEG and insufficient to pin the Fermi level, leading to a constant increase in e phi(B) with d(AlGaN). (C) 2010 American Institute of Physics. [doi: 10.1063/1.3481412]

    DOI: 10.1063/1.3481412

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  • Si Delta-Doped m-Plane AlGaN/GaN Heterojunction Field-Effect Transistors Reviewed

    Tetsuya Fujiwara, Stacia Keller, Masataka Higashiwaki, James S. Speck, Steven P. DenBaars, Umesh K. Mishra

    APPLIED PHYSICS EXPRESS   2 ( 6 )   1 - 61003   2009.06( ISSN:1882-0778

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    Transistor operation was demonstrated on non-polar Si delta-doped m-plane AlGaN/GaN hetero-junction field effect transistors (HFETs) grown by metal organic chemical vapor phase deposition. A maximum drain-source current of 340 mA/mm at a gate-source voltage (V(gs)) of +1 V, threshold voltage of -3 V and a maximum transconductance of 95 mS/mm at V(gs) = -1.4 V were exhibited. With increasing Si delta-doping, the sheet carrier concentration increased from 3.1 X 10(12) to 4.8 x 10(12) cm(-2). Good control of sheet carrier concentration by Si delta-doping was observed in non-polar m-plane AlGaN/GaN heterostructures. (C) 2009 The Japan Society of Applied Physics

    DOI: 10.1143/APEX.2.061003

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  • Effect of Dielectric Thickness on Power Performance of AlGaN/GaN HEMTs Reviewed

    Yi Pei, Siddharth Rajan, Masataka Higashiwaki, Zhen Chen, Steven P. Denlaars, Umesh K. Mishra

    IEEE ELECTRON DEVICE LETTERS   30 ( 4 )   313 - 315   2009.04( ISSN:0741-3106

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    The effect of SIN. passivation thickness on the power performance of AlGaN/GaN high-electron-mobility transistors (HEMTs) has been studied. A model is proposed to explain the surface-state dispersion and passivation of AlGaN/GaN HEMTs. Based on this model, a multidielectic passivation method has been proposed and demonstrated to both provide lower dielectric capacitance and help remove dc-RIF dispersion.

    DOI: 10.1109/LED.2009.2012444

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  • A comparative study of effects of SiNx deposition method on AlGaN/GaN heterostructure field-effect transistors Reviewed

    Masataka Higashiwaki, Zhen Chen, Rongming Chu, Yi Pei, Stacia Keller, Umesh K. Mishra, Nobumitsu Hirose, Toshiaki Matsui, Takashi Mimura

    APPLIED PHYSICS LETTERS   94 ( 5 )   53513   2009.02( ISSN:0003-6951

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    The effects of thin SiNx deposition on AlGaN/GaN heterostructure field-effect transistors were systematically studied by comparing their electrical and device characteristics. Two aspects of the thin SiNx film deposition were investigated: (i) the increase in two-dimensional electron gas (2DEG) density at the heterointerface and (ii) its capability as a gate insulating layer. Three different SiNx deposition methods were studied: catalytic chemical vapor deposition (Cat-CVD), metalorganic chemical vapor deposition (MOCVD), and plasma enhanced chemical vapor deposition (PECVD). A large increase in 2DEG density was obtained after SiNx deposition for all methods. The devices with MOCVD SiNx gate insulator showed a larger gate leakage current than those with the Cat-CVD and PECVD SiNx, implying that a thinning of the AlGaN surface barrier occurred due to Si diffusion into the AlGaN barrier during the high-temperature MOCVD process.

    DOI: 10.1063/1.3079798

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  • Enhancement-Mode m-plane AlGaN/GaN Heterojunction Field-Effect Transistors Reviewed

    Tetsuya Fujiwara, Siddharth Rajan, Stacia Keller, Masataka Higashiwaki, James S. Speck, Steven P. DenBaars, Umesh K. Mishra

    APPLIED PHYSICS EXPRESS   2 ( 1 )   1 - 11001   2009.01( ISSN:1882-0778

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    The first demonstration of the m-plane AlGaN/GaN heterojunction field-effect transistor was reported. This transistor exhibited enhancement-mode operation, with the threshold voltage of +2.0 V owing to the nonpolar AlGaN/GaN heterojunction. The maximum drain-source current density and the maximum transconductance were 130 mA/mm at a gate-source voltage (V(gs)) of +9V and 25 mS/mm at V(gs) = +8V, respectively. The on-to-off ratio was over 10(6). (C) 2009 The Japan Society of Applied Physics

    DOI: 10.1143/APEX.2.011001

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  • Development of high-frequency GaNHFETs for millimeter-wave applications Invited Reviewed

    Masataka Higashiwaki, Takashi Mimura, Toshiaki Matsui

    IEICE TRANSACTIONS ON ELECTRONICS   E91C ( 7 )   984 - 988   2008.07( ISSN:0916-8524

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    This paper describes the device fabrication process and characteristics of AlGaN/GaN heterostructure field-effect transistors (HFETs) aimed for millimeter-wave applications. We developed three novel techniques to suppress short-channel effects and thereby enhance high-frequency device characteristics: high-Al-composition and thin AlGaN barrier layers, SiN passivation by catalytic chemical vapor deposition, and sub-100-nm Ti-based gates. The Al0.4Ga0.6N/GaN HFETs with a gate length of 30 nm had a maximum drain current density of 1.6 A/mm and a maximum transconductance of 402 mS/mm. The use of these techniques led to a current-gain cutoff frequency of 181 GHz and a maximum oscillation frequency of 186 GHz.

    DOI: 10.1093/ietele/e91-c.7.984

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  • Development of high-frequency GaNHFETs for millimeter-wave applications Reviewed

    Masataka Higashiwaki, Takashi Mimura, Toshiaki Matsui

    IEICE TRANSACTIONS ON ELECTRONICS   E91C ( 7 )   984 - 988   2008.07( ISSN:0916-8524

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    This paper describes the device fabrication process and characteristics of AlGaN/GaN heterostructure field-effect transistors (HFETs) aimed for millimeter-wave applications. We developed three novel techniques to suppress short-channel effects and thereby enhance high-frequency device characteristics: high-Al-composition and thin AlGaN barrier layers, SiN passivation by catalytic chemical vapor deposition, and sub-100-nm Ti-based gates. The Al0.4Ga0.6N/GaN HFETs with a gate length of 30 nm had a maximum drain current density of 1.6 A/mm and a maximum transconductance of 402 mS/mm. The use of these techniques led to a current-gain cutoff frequency of 181 GHz and a maximum oscillation frequency of 186 GHz.

    DOI: 10.1093/ietele/e91-c.7.984

  • AlGaN/GaN heterostructure field-effect transistors on 4H-SiC substrates with current-gain cutoff frequency of 190GHz Reviewed

    Masataka Higashiwaki, Takashi Mimura, Toshiaki Matsui

    APPLIED PHYSICS EXPRESS   1 ( 2 )   1 - 21103   2008.02( ISSN:1882-0778

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    We report on state-of-the-art AlGaN/GaN heterostructure field-effect transistor (HFET) technology in the scope of millimeter-wave applications. 60-nm-long-gate HFETs having 4- and 6-nm-thick Al(0.4)Ga(0.6)N barrier layers and SiN passivation layers formed by catalytic chemical vapor deposition (Cat-CVD) were fabricated on 4H-SiC substrates. Both structures had low sheet resistances of 200-220 Omega/sq that were due to not only high mobilities of 1900 - 2000 cm(2)/(V.s) but also high electron densities of (1.4 - 1.7) x 10(13) cm (- 2), which were provided by the high-Al-composition barrier layers and the Cat-CVD SiN. The devices with the 4- and 6-nm-thick barriers had maximum drain current densities of 1.4 and 1.6 A/mm and peak extrinsic transconductances of 448 and 424 mS/mm, respectively. Maximum f(T) and f(max) reached 190 and 251 GHz, respectively. (c) 2008 The Japan Society of Applied Physics.

    DOI: 10.1143/APEX.1.021103

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  • GaN-based FETs using Cat-CVD SiN passivation for millimeter-wave applications Invited Reviewed

    Masataka Higashiwaki, Takashi Mimura, Toshiaki Matsui

    THIN SOLID FILMS   516 ( 5 )   548 - 552   2008.01( ISSN:0040-6090

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    We have found that SiN passivation by catalytic chemical vapor deposition (Cat-CVD) can significantly increase an electron density of an AlGaN/GaN heterostructure field-effect transistor (HFET). This effect enables thin-barrier HFET structures to have a high-density two-dimensional electron gas and leads to suppression of short-channel effects. We fabricated 30-nm-gate Al0.4Ga0.6N(8 nm)/GaN HFETs using Cat-CVD SiN. The maximum drain current density and extrinsic transconductance were 1.49 A/mm and 402 mS/mm, respectively. Current-gain cutoff frequency and maximum oscillation frequency of the HFETs were 181 and 186 GHz, respectively. These high-frequency device characteristics are sufficiently high enough for millimeter-wave applications. (C) 2007 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.tsf.2007.06.090

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  • Millimeter-wave GaNHFET technology Reviewed

    Masataka Higashiwaki, Takashi Mimura, Toshiaki Matsui

    GALLIUM NITRIDE MATERIALS AND DEVICES III   6894   L8941   2008( ISSN:0277-786X

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    This paper describes device process and characteristics of sub-100-nm-gate AlGaN/GaN heterostructure field-effect transistors (HFETs) for millimeter-wave applications. We developed three techniques to suppress short-channel effects and thereby enhance high-frequency device characteristics: high-Al-composition and thin AlGaN barrier layers, SiN passivation by catalytic chemical vapor deposition, and sub-100-nm Ti-based gates. The Al0.4Ga0.6N(6 nm)/GaN HFETs with a gate length of 60 nm on a 4H-SiC substrate showed a maximum drain current density of 1.6 A/mm and a maximum transconductance of 424 mS/mm. The use of the techniques led to record current-gain cutoff frequency (f(T)) and maximum oscillation frequency (f(max)) of 190 and 241 GHz, respectively. The f(T) and f(max) kept high values over the wide range of drain voltage and current. These results indicate significantly high potential of GaN HFETs for high-power applications in the millimeter-wave frequency range.

    DOI: 10.1117/12.767574

  • A comparative study of SiN deposition methods for millimeter-wave AlGaN/GaN HFETs Reviewed

    Masataka Higashiwaki, Zhen Chen, Yi Pei, Rongming Chu, Stacia Keller, Nobumitsu Hirose, Takashi Mimura, Toshiaki Matsui, Umesh K. Mishra

    Device Research Conference - Conference Digest, DRC   207 - 208   2008( ISSN:1548-3770

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    DOI: 10.1109/DRC.2008.4800805

  • Development of millimeter-wave GaNHFET technology Reviewed

    M. Higashiwaki, T. Mimura, T. Matsui

    PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE   204 ( 6 )   2042 - 2048   2007.06( ISSN:1862-6300

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    This paper describes approaches that we have used to improve the high-frequency device characteristics of GaN-based heterostructure field-effect transistors (HFETs). We developed three novel techniques to suppress short-channel effects: high-Al-composition and thin barrier layers, SiN passivation by catalytic chemical vapor deposition, and sub-100-nm Ti-based gates. These techniques were used to enhance the high-frequency device characteristics of Al-0.4 Ga-0.6 N/GaN HFETs, which had a record current-gain cutoff frequency of 181 GHz. In addition, high-performance depletion- and enhancement-mode AlN/GaN HFETs, which had DC and RF device characteristics fully comparable with those of state-of-the-art AlGaN/GaN HFETs, were also fabricated with these techniques. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

    DOI: 10.1002/pssa.200674860

  • Erratum: "High-Performance short-gate InAIN/GaN heterostructure field-effect transistors" (vol 45, pg L843, 2006) Reviewed

    Masataka Higashiwaki, Takashi Mimura, Toshiaki Matsui

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS   46 ( 20-24 )   L502 - L502   2007.06( ISSN:0021-4922

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    DOI: 10.1143/JJAP.46.L502

  • Enhancement-mode AlN/GaN HFETs using Cat-CVD SiN Reviewed

    Masataka Higashiwaki, Takashi Mimura, Toshiaki Matsui

    IEEE TRANSACTIONS ON ELECTRON DEVICES   54 ( 6 )   1566 - 1570   2007.06( ISSN:0018-9383

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    High-performance enhancement-mode (E-mode) AIN (2.5 nm)/GaN heterostructure field-effect transistors (HFETs) were fabricated with a novel method using SiN passivation by catalytic chemical vapor deposition (Cat-CVD). We found that the formation of a 2-D electron gas (2DEG) in the AIN/GaN heterostructure can be controlled by the presence of the Cat-CVD SiN on the barrier layer. Before SiN deposition, the 2DEG at the AIN/GaN heterointerface was completely depleted because of the extremely thin barrier layer. On the other hand, after SiN deposition, the decrease in AIN surface barrier height induced a high-density 2DEG. The E-mode HFETs with gate lengths of 100-180 nm and threshold voltages from +0.14 to +0.55 V showed a maximum drain-current density of 0.70-0.92 A/mm and a maximum extrinsic transconductance of 362-400 mS/mm. A current-gain cutoff frequency of 87 GHz and maximum oscillation frequency of 149 GHz were obtained for the 100-nm-gate devices.

    DOI: 10.1109/TED.2007.896607

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  • Reduction in potential barrier height of AlGaN/GaN heterostructures by SiN passivation Reviewed

    N. Onojima, M. Higashiwaki, J. Suda, T. Kimoto, T. Mimura, T. Matsui

    JOURNAL OF APPLIED PHYSICS   101 ( 4 )   043703   2007.02( ISSN:0021-8979

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    SiN passivation on AlGaN/GaN heterostructures was carried out using catalytic or plasma-enhanced chemical vapor deposition (Cat-CVD or PECVD), which has been found to increase two-dimensional electron gas (2DEG) density. The 2DEG density can be closely related to AlGaN surface properties via polarization effects. AlGaN potential barrier heights of AlGaN/GaN heterostructures with and without SiN passivation were systematically investigated using x-ray photoelectron spectroscopy (XPS) and capacitance-voltage (C-V) measurements. The results for the XPS and C-V measurements were consistent and demonstrated that a reduction in the AlGaN potential barrier height was actually induced by SiN passivation. Furthermore, Cat-CVD SiN passivation lowered the AlGaN potential barrier height more significantly than PECVD SiN passivation did, suggesting that the passivation method can influence the AlGaN potential barrier height.

    DOI: 10.1063/1.2472255

  • XPS study of surface potential in AlGaN/GaN heterostructure with Cat-CVD SiN passivation Reviewed

    N. Onojima, M. Higashiwaki, T. Matsui, T. Mimura, J. Suda, T. Kimoto

    PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 4 NO 7 2007   4 ( 7 )   2354 - +   2007( ISSN:1862-6351

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    AlGaN surface potentials in AlGaN/GaN heterostructures with and without SiN passivation were investigated using x-ray photoelectron spectroscopy (XPS). SiN films were formed on AlGaN surfaces by catalytic chemical vapor deposition (Cat-CVD), which has already been found to increase two-dimensional electron gas (2DEG) density. Based on a simple electrostatic analysis, the 2DEG density is expected to increase as the AlGaN surface potential decreases. This study experimentally demonstrates that a reduction in the AlGaN surface potential is actually induced by Cat-CVD SiN passivation. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

    DOI: 10.1002/pssc.200674757

  • Development of millimeter-wave GaN HFET technology Invited Reviewed

    M. Higashiwaki, T. Mimura, T. Matsui

    phys. stat. sol. (a)   204 ( 6 )   2042 - 2048   2007( ISSN:0031-8965

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    DOI: 10.1002/pssa.200674860

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  • 30-nm-gate AlGaN/GaN heterostructure field-effect transistors with a current-gain cutoff frequency of 181 GHz Reviewed

    Masataka Higashiwaki, Takashi Mimura, Toshiaki Matsui

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS   45 ( 42-45 )   L1111 - L1113   2006.11( ISSN:0021-4922

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    We fabricated Al0.4Ga0.6N(8 nm)/GaN heterostructure field-effect transistors (HFETs) with a gate length (L-G) of 30 nm on a sapphire substrate. The AlGaN/GaN HFETs, which had a 2-nm-thick SiN passivation and gate-insulating layer formed by catalytic chemical vapor deposition, showed a maximum drain current density of 1.49 A/mm, a peak extrinsic transconductance of 402 mS/mm, a current-gain cutoff frequency (f(T)) of 181 GHz, and a maximum oscillation frequency of 186 GHz. From a delay time analysis of f(T) for the HFETs with L-G = 30-150 nm, the electron velocity overshoot was not observed even when L-G was decreased to 30 nm.

    DOI: 10.1143/JJAP.45.L1111

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  • AlN/GaN insulated-gate HFETs using Cat-CVD SiN Reviewed

    Masataka Higashiwaki, Takashi Mimura, Toshiaki Matsui

    IEEE ELECTRON DEVICE LETTERS   27 ( 9 )   719 - 721   2006.09( ISSN:0741-3106

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    The authors fabricated SiN/AIN/GaN metalinsulator-semiconductor heterostructure field-effect transistors (MIS-HFETs) using SiN passivation by catalytic chemical vapor deposition (Cat-CVD). Cat-CVD SiN increased the electron density of AIN/GaN HFETs by compensating the surface depletion of the two-dimensional electron gas. The MIS-HFETs had a maximum drain current density of 0.95 A/mm and a peak extrinsic transconductance of 211 mS/mm. A current-gain cutoff frequency of 107 GHz and maximum oscillation frequency of 171 GHz were obtained for the 60- and 70-nm-gate devices, respectively.

    DOI: 10.1109/LED.2006.881087

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  • High-performance short-gate InAIN/GaN heterostructure field-effect transistors Reviewed

    Masataka Higashiwaki, Takashi Mimura, Toshiaki Matsui

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS   45 ( 29-32 )   L843 - L845   2006.08( ISSN:0021-4922

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    We fabricated 60-nm-gate InAlN/GaN heterostructure field-effect transistors (HFETs), which had a 6-nm-thick InAlN barrier with an Al composition of 0.86. The devices had a maximum drain current density of 1.34 A/mm and a maximum extrinsic transconductance of 389 mS/mm. The small-signal performance of the devices shoved a current-gain cutoff frequency of 172 GHz and a maximum oscillation frequency of 206 GHz. These DC and RF device characteristics were superior to the best values reported for AlGaN (8nm)/GaN HFETs with the same gate length.

    DOI: 10.1143/JJAP.45.L843

  • Effects of SiN passivation by catalytic chemical vapor deposition on electrical properties of AlGaN/GaN heterostructure field-effect transistors Reviewed

    Masataka Higashiwaki, Norio Onojima, Toshiaki Matsui, Takashi Mimura

    JOURNAL OF APPLIED PHYSICS   100 ( 3 )   2006.08( ISSN:0021-8979

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    We investigated the effects of SiN passivation by catalytic chemical vapor deposition (Cat-CVD) on the electrical properties of AlGaN/GaN heterostructure field-effect transistors. The two-dimensional electron density (N-s) greatly increased after the Cat-CVD SiN deposition, and the tendency of the increase was enhanced with decreasing AlGaN barrier thickness. As a result of the large increase in Ns, the sheet resistance (R-sh) significantly decreased after the deposition, and it had low values of 320-460 ohm/square for extremely thin AlGaN barriers of 4 - 10 nm. The increase in Ns showed little dependence on SiN thickness, indicating that the stress applied to the AlGaN barrier by SiN cannot be the origin of the increase. Cat-CVD SiN also improved the in-plane uniformity of mobility for extremely thin-barrier structures, which in turn improved the uniformity of Rsh. Moreover, we found that Cat-CVD was more effective than plasma-enhanced chemical vapor deposition in increasing Ns. A comparison of theoretical calculations and experimental results indicated that these behaviors can be explained by a decrease in the AlGaN surface barrier height due to the SiN deposition. (c) 2006 American Institute of Physics.

    DOI: 10.1063/1.2218759

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  • Superconductivity of InN with a well defined Fermi surface Invited Reviewed

    T. Inushima, N. Kato, D. K. Maude, Hai Lu, W. J. Schaff, R. Tauk, Y. Meziani, S. Ruffenack, O. Briot, W. Knap, B. Gil, H. Miwa, A. Yamamoto, D. Muto, Y. Nanishi, M. Higashiwaki, T. Matsui

    PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS   243 ( 7 )   1679 - 1686   2006.06( ISSN:0370-1972

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    In this report we present our recent investigation on the co-existence of superconducting and semiconducting properties in InN grown on sapphire (0001) by the use of MBE and MOCVD methods. Magneto-transport measurements were done using InN with a carrier density n. from 4 x 10(17) to 4 x 102 cm 3 in the temperature range from 20 mK to 2 K and under the magnetic field (B) up to 23 T(c) As a result, even InN samples with n, as low as 4 x 10(17) cm(-3) showed superconductivity at T(c) = 0.12 K. The vortex solid of InN was melted by thermal fluctuation and by the external field, similarly to the observation in layered high T(c) superconductors. By the Shubnikov-de Haas oscillation measurements it was found that there were substantial carriers spread in the a-b plane which played an essential role not only for the occurrence of the superconductivity, but also for many other unexpected electronic and optical properties of InN. Based on these results we present a possible mechanism of superconductivity in terms of the interaction between the conduction electrons and the fixed d-electrons of In atoms spread in the a-b plane. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

    DOI: 10.1002/pssb.200565419

  • High f(T) and f(max) AlGaN/GaN HFETs achieved by using thin and high-Al-composition AlGaN barrier layers and Cat-CVD SiN passivation Reviewed

    M. Higashiwaki, N. Onojima, T. Matsui, T. Mimura

    PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE   203 ( 7 )   1851 - 1855   2006.05( ISSN:1862-6300

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    We fabricated sub-0.1 mu m-gate Al0.4Ga0.6N/GaN heterostructure field-effect transistors (HFETs) with AlGaN barrier thicknesses of 4-10 nm. The devices were passivated with 2 nm-thick SiN layers formed by catalytic chemical vapor deposition (Cat-CVD). The Cat-CVD SiN passivation greatly increased electron density, and the effect became more significant with decreasing AlGaN barrier thickness. The HFETs had maximum drain current densities of 1.1-1.5A/mm and peak extrinsic transconductances of 305-438 mS/mm. Peak current-gain cutoff frequency of 163 GHz and maximum oscillation frequency of 192 GHz were obtained for the devices with 8 nm-thick AlGaN barriers. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

    DOI: 10.1002/pssa.200565199

  • High sensitivity and quantitative magnetic field measurements at 600 degrees C Reviewed

    Takuya Yamamura, Dai Nakamura, Masataka Higashiwaki, Toshiaki Matsui, Adarsh Sandhu

    JOURNAL OF APPLIED PHYSICS   99 ( 8 )   2006.04( ISSN:0021-8979

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    High sensitivity micro-Hall sensors were fabricated using AlGaN/GaN two-dimensional electron gas heterostructures grown by molecular beam epitaxy for high temperature operation. The room temperature electron mobility and sheet carrier concentration of the heterostructures were 850 cm(2)/V s and 7.7x10(12) cm(-2), respectively. The Hall voltage increased linearly with applied magnetic field up to 0.5 T for all temperatures in the range of temperature from 20 to 600 degrees C. A 100 mu mx100 mu m Hall device with a magnetic sensitivity of 0.35 G/(Hz)(1/2) at 600 degrees C was used to measure the Curie temperature of NdFeB. The AlGaN/GaN micro-Hall sensors will find a wide range of applications including high temperature scanning Hall microscopy, monitoring rotating parts in the engines of automobiles as well as space vehicles which are exposed to extreme changes in temperature and radiation. (C) 2006 American Institute of Physics.

    DOI: 10.1063/1.2158693

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  • AlGaN/GaN MIS HFETs with f(T) of 163 GHz using Cat-CVD SiN gate-insulating and passivation layers Reviewed

    M Higashiwaki, T Matsui, T Mimura

    IEEE ELECTRON DEVICE LETTERS   27 ( 1 )   16 - 18   2006.01( ISSN:0741-3106

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    Al0.4Ga0.6N/GaN heterostructure field-effect transistors (HFETs) with an AlGaN barrier thickness of 8 nm and a gate length (L-G) of 0.06-0.2 mu m were fabricated on a sapphire substrate. We employed two novel techniques, which were thin, high-Al-composition AlGaN barrier layers and SiN gate-insulating, passivation layers formed by catalytic chemical vapor deposition, to enhance high-frequency device characteristics by suppressing the short channel effect. The HFETs with L-G = 0.06-0.2 mu m had a maximum drain current density of 1.17-1.24 A/mm at a gate bias of +1.0 V and a peak extrinsic transconductance of 305-417 mS/mm. The current-gain cutoff frequency (f(T)) was 163 GHz, which is the highest value to have been reported for GaN HFETs. The maximum oscillation frequency (f(max)) was also high, and its value derived from the maximum stable gain or unilateral gain was 192 or 163 GHz, respectively.

    DOI: 10.1109/LED.2005.860884

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  • Superconductivity of InN observed in the magnetoresistance at low temperature Reviewed

    T. Inushima, N. Kato, T. Takenobu, M. Motokawa, M. Higashiwaki, T. Matsui

    YAMADA CONFERENCE LX ON RESEARCH IN HIGH MAGNETIC FIELDS   51   279 - +   2006( ISSN:1742-6588

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    We report on the superconductivity of n-type InN. There is an optimum carrier density for the occurrence of the superconductivity. The lowest carrier density is limited by the Mott transition of n(c) =2 x 10(17) cm(-3) and the highest density is limited by the superconductivity to metal transition of n(i) similar to 7 x 10(20) cm(-3). We propose a mechanism where the occurrence of the superconductivity is related to the presence of In-In chains of finite lengths in the ab plane. The In-In chains, which originate from the inversion domains of InN grown on sapphire (0001) and elongate along [1120], are coupled to form micro Josephson-junctions.

    DOI: 10.1088/1742-6596/51/1/064

  • High fT and fmax AlGaN/GaN HFETs achieved by using thin and high-Al-composition AlGaN barrier layers and Cat-CVD SiN passivation Reviewed

    M. Higashiwaki, N. Onojima, T. Matsui, T. Mimura

    phys. stat. sol. (a)   203 ( 7 )   1851 - 1855   2006( ISSN:0031-8965

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    DOI: 10.1002/pssa.200565199

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  • 120-nm-T-shaped-Mo/Pt/Au-gate AlGaN/GaN high electron mobility transistors Reviewed

    Y Yamashita, A Endoh, K Ikeda, K Hikosaka, T Mimura, M Higashiwaki, T Matsui, S Hiyamizu

    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B   23 ( 5 )   L13 - L15   2005.09( ISSN:1071-1023

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    We fabricated 120-nm-T-shaped-Mo/Pt/Au-gate AlGaN/GaN high electron mobility transistors (HEMTs) on sapphire substrates. The gate leakage current I-gs of the Mo/Pt/Au-gate HEMT at a gate-source voltage V-gs of -5 V was as much as five orders of magnitude lower than that of the Ni/Pt/Au-gate HEMT under the as-deposited condition. The off-state breakdown voltage, defined as the gate-source voltage when the gate-source current is -1 mA/mm, was about -60 V for the Mo/Pt/Au-gate HEMT. These dc performances are comparable to those of the Ni/Pt/Au-gate HEMTs in which the Schottky contacts were improved with rapid thermal annealing at 500 degrees C. The Mo/Pt/Au-gate HEMTs also exhibited good rf performance without RTA. The cutoff frequency f(T) was more than 50 GHz and the maximum oscillation frequency f(max) was about 100 GHz. (c) 2005 American Vacuum Society.

    DOI: 10.1116/1.2013315

  • Electron density dependence of the electronic structure of InN epitaxial layers grown on sapphire (0001) Reviewed

    T. Inushima, M. Higashiwaki, T. Matsui, T. Takenobu, M. Motokawa

    Physical Review B - Condensed Matter and Materials Physics   72 ( 8 )   2005.08( ISSN:1098-0121

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    The temperature dependence of the resistivity of InN was investigated as a function of carrier density. The carrier density was changed from ne =1.8× 1018 cm-3 to 1.5× 1019 cm-3 by Si doping. The InN investigated showed metallic conduction above 20 K. At lower temperatures there was a resistivity anomaly originating from carrier localization in the a-b plane, which was confirmed by the magnetoresistance at 0.5 K. The Shubnikov-de Haas oscillation showed that InN had a spherical Fermi surface and its radius increased according to the increase of ne when ne &lt
    5× 1018 cm-3. In addition, an oscillation corresponding to the constant carrier density of 4.5× 1012 cm-2 was observed in the field applied perpendicular to the a-b plane. This oscillation showed an anomalous angle dependence on the magnetic field. Taking into account this density, we determined the critical carrier density of the Mott transition to be 2× 1017 cm-3. Anisotropy of localization was observed within the a-b plane, which indicates that the distribution of the electrons was not uniform in the a-b plane. The ne dependence of the magnetoresistance revealed an electronic structure change around 5× 1018 cm-3. From these results, an electronic structure at the fundamental absorption edge of InN grown on sapphire (0001) was presented. © 2005 The American Physical Society.

    DOI: 10.1103/PhysRevB.72.085210

  • Electron density dependence of the electronic structure of InN epitaxial layers grown on sapphire (0001) Reviewed

    T Inushima, M Higashiwaki, T Matsui, T Takenobu, M Motokawa

    PHYSICAL REVIEW B   72 ( 8 )   085210   2005.08( ISSN:2469-9950

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    The temperature dependence of the resistivity of InN was investigated as a function of carrier density. The carrier density was changed from n(e)=1.8x10(18) cm(-3) to 1.5x10(19) cm(-3) by Si doping. The InN investigated showed metallic conduction above 20 K. At lower temperatures there was a resistivity anomaly originating from carrier localization in the a-b plane, which was confirmed by the magnetoresistance at 0.5 K. The Shubnikov-de Haas oscillation showed that InN had a spherical Fermi surface and its radius increased according to the increase of n(e) when n(e)&lt; 5x10(18) cm(-3). In addition, an oscillation corresponding to the constant carrier density of 4.5x10(12) cm(-2) was observed in the field applied perpendicular to the a-b plane. This oscillation showed an anomalous angle dependence on the magnetic field. Taking into account this density, we determined the critical carrier density of the Mott transition to be 2x10(17) cm(-3). Anisotropy of localization was observed within the a-b plane, which indicates that the distribution of the electrons was not uniform in the a-b plane. The n(e) dependence of the magnetoresistance revealed an electronic structure change around 5x10(18) cm(-3). From these results, an electronic structure at the fundamental absorption edge of InN grown on sapphire (0001) was presented.

    DOI: 10.1103/PhysRevB.72.085210

  • Effect of thermal annealing on 120-nm-T-shaped-Ti/Pt/Au-gate AlGaN/GaN high electron mobility transistors Reviewed

    Y Yamashita, A Endoh, K Ikeda, K Hikosaka, T Mimura, M Higashiwaki, T Matsui, S Hiyamizu

    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B   23 ( 3 )   895 - 899   2005.05( ISSN:1071-1023

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    We fabricated 120-nm-long-T-shaped-Ti/Pt/Au-gate AlGaN/GaN high electron mobility transistors (HEMTs) on sapphire substrates and annealed them thermally to improve their Schottky contacts (i.e., to reduce interface traps, increase the Schottky barrier height, and get better adhesion), thereby reducing gate leakage current, achieving better gate controllability, and obtaining better dc and rf characteristics compared to the HEMTs with as-deposited Schottky gate metals. Rapid thermal annealing (RTA) was carried out successively at 500, 600, and 650 degrees C. The drain-source current I-ds decreased with RTA temperature up to 600 degrees C and turned to increase at 650 degrees C. The maximum transconductance g(m_max), on the other hand, increased up to 650 degrees C, indicating that RTA improved the dc characteristics of the HEMTs. We confirmed the improvement of Schottky contacts by measuring gate leakage current I-gs and calculating the Schottky barrier height phi(B). After RTA at 600 degrees C, the I-gs at a gate-source voltage V-gs of -10 V was as much as three orders of magnitude lower than it was in the as-deposited condition and the phi(B) was 0.27 eV greater than it was in the as-deposited condition (1.16 eV versus 0.89 eV). After the RTA at 650 degrees C, the phi(B) was slightly less than it was after the RTA at 600 degrees C. RTA at 600 and 650 degrees C also improved the rf characteristics, increasing the cutoff frequency f(T) from 80 to 84 GHz (5% increase) and increasing the maximum oscillation frequency f(max) from 102 to M GHz (20% increase). (c) 2005 American Vacuum Society.

    DOI: 10.1116/1.1897706

  • Cat-CVD SiN-passivated AlGaN-GaNHFETs with thin and high al composition barrier layers Reviewed

    M Higashiwaki, N Hirose, T Matsui

    IEEE ELECTRON DEVICE LETTERS   26 ( 3 )   139 - 141   2005.03( ISSN:0741-3106

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    The effect of SiN surface passivation by catalytic chemical vapor deposition (Cat-CVD) on Al0.4Ga0.6N-GaN heterostructure field-effect transistors (HFETs) was investigated. The channel sheet resistance was reduced by the passivation due to an increase in electron density, and the device characteristics of the thin-barrier HFETs were significantly improved by the reduction of source and drain resistances. The AlGaN(8 nm)-AlN(1.3 nm)-GaN HFET device with a source/drain distance of 3 mum and a gate length of 1 um had a maximum drain current density of 0.83 Mum at a gate bias of +1.5 V and an extrinsic maximum transconductance of 403 mS/mm. These results indicate the substantial potential of Cat-CVD SiN-passivated AlGaN-GaN HFETs with thin and high Al composition barrier layers.

    DOI: 10.1109/LED.2004.842736

    CiNii Article

  • Vacancy-type defects in Si-doped InN grown by plasma-assisted molecular-beam epitaxy probed using monoenergetic positron beams Reviewed

    A Uedono, SF Chichibu, M Higashiwaki, T Matsui, T Ohdaira, R Suzuki

    JOURNAL OF APPLIED PHYSICS   97 ( 4 )   043514   2005.02( ISSN:0021-8979

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    High-quality InN layers grown on sapphire substrates by plasma-assisted molecular-beam epitaxy were characterized using monoenergetic positron beams. The carrier concentrations of the films were controlled by Si doping (2.1x10(18) to 1.4x10(19) cm(-3)), and the highest obtained Hall mobility was 1300 cm(2) V-1 s(-1). The Doppler broadening spectra of the annihilation radiation and the lifetime spectra of positrons were measured as a function of the incident positron energy for undoped and Si-doped InN films. The line-shape parameter S increased with increasing carrier concentration, suggesting the introduction of vacancy-type defects by a Fermi-level effect. The major defect species were varied with carrier concentration, and its species were identified as In vacancies (V-In) or their related defects. (C) 2005 American Institute of Physics.

    DOI: 10.1063/1.1845575

  • MBE growth and device characteristics of InAIN/GaN HFETs Reviewed

    M Higashiwaki, T Matsui

    Physica Status Solidi C - Conferences and Critical Reviews, Vol 2, No 7   2 ( 7 )   2598 - 2601   2005( ISSN:1610-1634

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    InAlN/GaN heterostructure field-effect transistors (HFETs) were grown on sapphire substrates by plasma-assisted molecular-beam epitaxy. The In mole fraction in InAlN was estimated to be 0.15 from the X-ray diffraction profile. The room-temperature Hall mobility was 654 cm(2) /V(.)s, and the sheet electron density was 2.0 x 10(13) cm(-2). The InAlN/GaN HFET device, which had a source-drain spacing of 3 mu m and a gate length of 1.5 mu m, showed a good DC performance and an excellent pinch-off characteristic. The maximum source-drain current density and extrinsic transconductance were 500 mA/mm and 52 mS/mm, respectively. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

    DOI: 10.1002/pssc.200461389

  • AlGaN/GaN heterostructure field-effect transistors with current gain cut-off frequency of 152 GHz on sapphire substrates Reviewed

    M Higashiwaki, T Matsui

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS   44 ( 16-19 )   L475 - L478   2005( ISSN:0021-4922

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    AlGaN/GaN heterostructure field-effect transistors (HFETs) with a gate length (L-G) of 60-250nm were fabricated on a sapphire substrate. The HFET structure was grown by plasma-assisted molecular-beam epitaxy, and a 2-nm-thick SiN film was formed on the device surface by catalytic chemical vapor deposition. All of the HFETs showed outstanding DC device performance. They exhibited maximum drain current densities of 1.50-1.55 A/mm and extrinsic transconductances of 340-400 mS/mm. The 60-nm-gate HFET had a current gain cut-off frequency (f(T)) of 152GHz and a maximum oscillation frequency (f(max)) of 173 GHz. To our knowledge, the f(T) and f(max) are the highest ever reported for GaN-based transistors. These superior high-frequency characteristics were achieved with a process using a thin and high-Al-content barrier layer, high-quality catalytic chemical vapor deposition (Cat-CVD) SiN passivation, and sub-0.1-mu m gates defined by electron-beam lithography.

    DOI: 10.1143/JJAP.44.L475

  • Cat-CVD SiN insulated-gate AlGaN/GaN HFETs with 163 GHz fT and 184 GHz fmax Reviewed

    M. Higashiwaki, T. Matsui, T. Mimura

    Device Research Conference - Conference Digest, DRC   2005   12   2005( ISSN:1548-3770

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    DOI: 10.1109/DRC.2005.1553161

  • AlGaN/GaN heterostructure field-effect transistors with current gain cut-off frequency of 152 GHz on sapphire substrates Reviewed

    M Higashiwaki, T Matsui

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS   44 ( 16-19 )   L475 - L478   2005( ISSN:0021-4922

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    AlGaN/GaN heterostructure field-effect transistors (HFETs) with a gate length (L-G) of 60-250nm were fabricated on a sapphire substrate. The HFET structure was grown by plasma-assisted molecular-beam epitaxy, and a 2-nm-thick SiN film was formed on the device surface by catalytic chemical vapor deposition. All of the HFETs showed outstanding DC device performance. They exhibited maximum drain current densities of 1.50-1.55 A/mm and extrinsic transconductances of 340-400 mS/mm. The 60-nm-gate HFET had a current gain cut-off frequency (f(T)) of 152GHz and a maximum oscillation frequency (f(max)) of 173 GHz. To our knowledge, the f(T) and f(max) are the highest ever reported for GaN-based transistors. These superior high-frequency characteristics were achieved with a process using a thin and high-Al-content barrier layer, high-quality catalytic chemical vapor deposition (Cat-CVD) SiN passivation, and sub-0.1-mu m gates defined by electron-beam lithography.

    DOI: 10.1143/jjap.44.L475

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  • Barrier thickness dependence of electrical properties and DC device characteristics of AlGaN/GaN heterostructure field-effect transistors grown by plasma-assisted molecular-beam epitaxy Reviewed

    M Higashiwaki, T Matsui

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS   43 ( 9A-B )   L1147 - L1149   2004.09( ISSN:0021-4922

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    We report on the barrier thickness dependence of the electrical properties and DC device characteristics of Al0.4Ga0.6N/GaN heterostructure field-effect transistors (HFETs). The HFET structures with 8-25-nm-thick AlGaN barrier layers were grown on sapphire substrates by plasma-assisted molecular-beam epitaxy. All of the fabricated HFET devices with a gate length of 1 mum showed a good DC performance and an excellent pinch-off characteristic. The extrinsic transconductance of the HFET devices increased from 185 to 360 mS/mm with decreasing AlGaN barrier thickness from 25 to 8 nm, while the maximum drain current for a gate bias of + 1.0 V decreased from 1.1 to 0.68 A/mm.

    DOI: 10.1143/JJAP.43.L1147

    CiNii Article

  • Estimation of band-gap energy of intrinsic InN from photoluminescence properties of undoped and Si-doped InN films grown by plasma-assisted molecular-beam epitaxy Reviewed

    M Higashiwaki, T Matsui

    JOURNAL OF CRYSTAL GROWTH   269 ( 1 )   162 - 166   2004.08( ISSN:0022-0248

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    InN films with electron densities of 1.6 x 10(18)-1.4 x 10(19) cm(-3) had photoluminescence (PL) properties with clear electron density dependencies. The PL peak shifted to a higher energy with increasing electron density, whereas PL intensity decreased with increasing electron density. These characteristics are typical of degenerate semiconductors with a large density of defects and/or dislocations. We estimated a band-gap energy of 0.6-0.65 eV for intrinsic InN from the shift in the PL peak position and band-gap shrinkage due to the conduction-band renormalization effect. (C) 2004 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.jcrysgro.2004.05.045

  • InAlN/GaN heterostructure field-effect transistors grown by plasma-assisted molecular-beam epitaxy Reviewed

    M Higashiwaki, T Matsui

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS   43 ( 6B )   L768 - L770   2004.06( ISSN:0021-4922

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    We report on the plasma-assisted molecular-beam epitaxy growth and device characteristics of InAIN/GaN heterostructure field-effect transistors (HFETs). The In mole fraction in InAIN was estimated to be 0.15 from the X-ray diffraction profile. The surface root-mean-square roughness of the InAIN layer was less than 3 nm. The room-temperature Hall mobility was 654 cm(2)/V.s, and the sheet electron density was 1.7 x 10(13) cm(-2). The InAIN/GaN HFET, which had a source-drain spacing of 3 mum and a gate length of 1.5 mum, showed a good pinch-off characteristic. The maximum source-drain current density and extrinsic transconductance were 500 mA/mm and 52 mS/mm, respectively.

    DOI: 10.1143/JJAP.43.L768

    CiNii Article

  • Non-recessed-gate enhancement-mode AlGaN/GaN high electron mobility transistors with high RF performance Reviewed

    A Endoh, Y Yamashita, K Ikeda, M Higashiwaki, K Hikosaka, T Matsui, S Hiyamizu, T Mimura

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS   43 ( 4B )   2255 - 2258   2004.04( ISSN:0021-4922

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    We fabricated non-recessed-gate enhancement-mode (E-mode) AlGaN/GaN high electron mobility transistors (HEMTs) with a gate length L-g of 120nm. As gate metals, Ni/Pt/Au and Mo/Pt/Au were used. The Ni/Pt/Au-gate HEMTs with rapid thermal annealing (RTA) at 500degreesC were normally-off at a gate-source voltage V-gs of 0 V, indicating E-mode operation. Moreover, the Mo/Pt/Au-gate HEMTs also showed E-mode device operation without RTA. The fabricated E-mode HEMTs with both gate metals showed high RF performance. We obtained a cutoff frequency f(T) of more than 50 GHz and a maximum oscillation frequency f(max) of approximately 100 GHz.

    DOI: 10.1143/JJAP.43.2255

    CiNii Article

  • Optical properties of Si-doped InN grown on sapphire (0001) Reviewed

    T. Inushima, M. Higashiwaki, T. Matsui

    Physical Review B - Condensed Matter and Materials Physics   68 ( 23 )   2003.12( ISSN:1550-235X

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    The carrier concentration dependence of the interaction between free carriers and longitudinal optical (LO) phonons of InN is studied by Raman scattering and Fourier transform infrared measurements. InN is grown on a sapphire (0001) surface by plasma-assisted molecular beam epitaxy. The carrier concentration is varied from 1.8 × 1018 to 1.5 × 1019 cm−3 by Si doping. The infrared reflection spectra, to which the vibration in the a − b plane contributes, reveal a linear coupling between the E1(LO) phonon and the plasma oscillation of the free carriers. From the plasma frequency the electron effective mass is estimated to be me⊥* = 0.085m0 for the intrinsic InN. The Raman spectra, to which the vibration along the c axis contributes, reveal that the A1(LO) phonon and free carriers couple nonlinearly, where a Fano interference between the zone-center LO phonon and the quasicontinuum electronic state along the c axis is prominent. With these results, the anisotropic electronic structure of InN is discussed. © 2003 The American Physical Society.

    DOI: 10.1103/PhysRevB.68.235204

  • Optical properties of Si-doped InN grown on sapphire (0001) Reviewed

    T Inushima, M Higashiwaki, T Matsui

    PHYSICAL REVIEW B   68 ( 23 )   2003.12( ISSN:2469-9950

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    The carrier concentration dependence of the interaction between free carriers and longitudinal optical (LO) phonons of InN is studied by Raman scattering and Fourier transform infrared measurements. InN is grown on a sapphire (0001) surface by plasma-assisted molecular beam epitaxy. The carrier concentration is varied from 1.8x10(18) to 1.5x10(19) cm(-3) by Si doping. The infrared reflection spectra, to which the vibration in the a-b plane contributes, reveal a linear coupling between the E-1(LO) phonon and the plasma oscillation of the free carriers. From the plasma frequency the electron effective mass is estimated to be m(eperpendicular to)(*)=0.085m(0) for the intrinsic InN. The Raman spectra, to which the vibration along the c axis contributes, reveal that the A(1)(LO) phonon and free carriers couple nonlinearly, where a Fano interference between the zone-center LO phonon and the quasicontinuum electronic state along the c axis is prominent. With these results, the anisotropic electronic structure of InN is discussed.

    DOI: 10.1103/PhysRevB.68.235204

  • Control of electron density in InN by Si doping and optical properties of Si-doped InN Reviewed

    M Higashiwaki, T Inushima, T Matsui

    PHYSICA STATUS SOLIDI B-BASIC RESEARCH   240 ( 2 )   417 - 420   2003.11( ISSN:0370-1972

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    We have studied Si-doping profiles of InN films grown by plasma-assisted molecular-beam epitaxy and their photoluminescence (PL) properties. We confirmed experimentally that Si acts as a donor in InN. Undoped and Si-doped InN films with electron densities (n) of 1.6 x 10(18) - 1.4 x 10(19) cm(-3) showed clear n dependences of PL properties. The PL peak shifted to the higher energy side with increasing n, and the PL intensity decreased with increasing n. These were characteristics of degenerated semiconductors with a large density of defects and/or dislocations. The band-gap energy of degenerated InN films with n = 1.6 x 10(18) - 4.7 x 10(18) cm(-3) was estimated to be about 0.6 eV by assuming a nonparabolic conduction band and a constant band-renormalization effect. By taking the band-gap shrinkage of about 20 meV due to the conduction-band renormalization into account, we suggest that the band-gap energy of intrinsic InN is 0.6-0.65 eV. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

    DOI: 10.1002/pssb.200303349

  • Epitaxial growth of high-quality InN films on sapphire substrates by plasma-assisted molecular-beam epitaxy Reviewed

    M Higashiwaki, T Matsui

    JOURNAL OF CRYSTAL GROWTH   252 ( 1-3 )   128 - 135   2003.05( ISSN:0022-0248

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    Studying the epitaxial growth of InN films by plasma-assisted molecular-beam epitaxy, we found a buffer layer formed with a low-temperature-grown GaN (LT-GaN) and a low-temperature-grown InN (LT-InN) layers to be effective for improving their structural and electrical properties. Not only the growth temperature of a main part of InN film but growth temperatures and thicknesses of LT-GaN and LT-InN layers strongly influenced InN film properties. The surface of a 260-nm-thick InN film grown at the optimum condition was smooth with the surface root-mean-square roughness less than 4 nm. Its Hall mobility and background electron density at room temperature were 1420 cm(2)/V s and 1.4 x 10(18) cm(-3), respectively. (C) 2003 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0022-0248(03)00918-7

    CiNii Article

  • Plasma-assisted MBE growth of InN films and InAlN/InN heterostructures Reviewed

    M Higashiwaki, T Matsui

    JOURNAL OF CRYSTAL GROWTH   251 ( 1-4 )   494 - 498   2003.04( ISSN:0022-0248

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    We have studied the growth of InN thin films and InAlN/InN heterostructures on a low-temperature grown GaN (LT-GaN) layer on a sapphire substrate by plasma-assisted molecular-beam epitaxy (PAMBE). Cross-sectional transmission electron microscopy revealed that the InN film stood on the LT-GaN layer like a bridge, indicating that the InN film was almost free standing. PL and optical absorption measurements of the InN film showed that the intrinsic band gap of hexagonal InN is less than 0.7 eV. We successfully grew coherent InAlN layers with an A] content up to 0.15 on the InN layer. This demonstrated that single-crystal InAlN/InN heterostructures can be grown by PAMBE. (C) 2002 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0022-0248(02)02362-X

  • Optical properties of Si-doped InN grown on sapphire (0001) Reviewed

    T. Inushima, M. Higashiwaki, T. Matsui

    Phys. Rev. B   68 ( 23 )   235204   2003( ISSN:0163-1829

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    DOI: 10.1103/PhysRevB.68.235204

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  • InP HEMTs: Physics, applications, and future Reviewed

    A. Endoh, Y. Yamashita, K. Shinohara, M. Higashiwaki, K. Hikosaka, T. Matsui, S. Hiyamizu, T. Mimura

    Device Research Conference - Conference Digest, DRC   2003-   5 - 8   2003( ISSN:1548-3770

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    In this paper, we review our recent results obtained for InP-based HEMTs. We have developed several fabrication techniques, and obtained an ultrahigh f&lt
    inf&gt
    T&lt
    /inf&gt
    of 562 GHz for a 25 nm long gate pseudomorphic InAlAs/InGaAs HEMT. We also discuss possible applications of our HEMTs and the future of InP-based HEMTs.

    DOI: 10.1109/DRC.2003.1226847

  • Electronic structure of InN observed by Shubnikov-de Haas measurements Reviewed

    T. Inushima, M. Higashiwaki, T. Matsui, T. Takenobu, M. Motokawa

    Physica Status Solidi C: Conferences   ( 7 )   2822 - 2825   2003( ISSN:1610-1634

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    We investigated the electronic structure of degenerated InN by Shubnikov-de Haas (SdH) measurements for the first time. The SdH oscillation depends on the angle between the crystal c-axis and the applied field and has two components
    one originates from the spherical Fermi surface with effective mass of about 0.085 m0, the other from the layered structure spread in the a-b plane. In the case of Sidoped InN with the carrier density of 2.5×1018 cm-3, about half electron density exists on the a-b plane. © 2003 WILEY-VCH Verlag GmbH &amp
    Co. KGaA.

    DOI: 10.1002/pssc.200303461

  • Fabrication of sub-50-nm-gate i-AlGaN/GaN HEMTs on sapphire Reviewed

    Akira Endoh, Yoshimi Yamashita, Keiji Ikeda, Masataka Higashiwaki, Kohki Hikosaka, Toshiaki Matsui, Satoshi Hiyamizu, Takashi Mimura

    Physica Status Solidi C: Conferences   ( 7 )   2368 - 2371   2003( ISSN:1610-1634

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    We fabricated sub-50-nm-gate i-AlGaN/GaN high electron mobility transistors (HEMTs) on sapphire and measured their DC and RF characteristics at room temperature. The fabricated HEMTs exhibited true device operation and good pinch-off characteristics down to a gate length Lg of 25 nm. For the HEMTs with a source-drain spacing Lsd of 2 μm, we obtained the Lg dependence of the cutoff frequency fT under a drain-source voltage Vds of 3 V. The peak fT was measured to be 102 GHz at Lg = 35 nm. At Lg = 25 nm, fT started to decrease due to the short-channel effect. The highest fT of 110 GHz was obtained by reducing Lsd from 2 to 1.5 μm and by increasing Vds from 3 to 4 V. © 2003 WILEY-VCH Verlag GmbH &amp
    Co. KGaA.

    DOI: 10.1002/pssc.200303335

  • Fabrication of sub-50-nm-gate i-AlGaN/GaN HEMTs on sapphire Reviewed

    A Endoh, Y Yamashita, K Ikeda, M Higashiwaki, K Hikosaka, T Matsui, S Hiyamizu, T Mimura

    5TH INTERNATIONAL CONFERENCE ON NITRIDE SEMICONDUCTORS (ICNS-5), PROCEEDINGS   0 ( 7 )   2368 - 2371   2003( ISSN:1862-6351

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    We fabricated sub-50-nm-gate i-AlGaN/GaN high electron mobility transistors (HEMTs) on sapphire and measured their DC and RF characteristics at room temperature. The fabricated HEMTs exhibited true device operation and good pinch-off characteristics down to a gate length L-g of 25 nm. For the HEMTs with a source-drain spacing L-sd of 2 mum, we obtained the Lg dependence of the cutoff frequency f(T) under a drain-source voltage V-ds of 3 V. The peak f(T) was measured to be 102 GHz at L-g = 35 nm. At L-g = 25 nm, f(T) started to decrease due to the short-channel effect. The highest fT of 110 GHz was obtained by reducing L-sd from 2 to 1.5 mum and by increasing V-ds from 3 to 4 V. (C) 2003 WILEY-VCH Vertag GmbH & Co. KGaA, Weinheim.

    DOI: 10.1002/pssc.200303335

  • Electronic structure of InN observed by Shubnikov-de Haas measurements Reviewed

    T Inushima, M Higashiwaki, T Matsui, T Takenobu, M Motokawa

    5TH INTERNATIONAL CONFERENCE ON NITRIDE SEMICONDUCTORS (ICNS-5), PROCEEDINGS   0 ( 7 )   2822 - 2825   2003( ISSN:1862-6351

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    We investigated the electronic structure of degenerated InN by Shubnikov-de Haas (SdH) measurements for the first time. The SdH oscillation depends on the angle between the crystal c-axis and the applied field and has two components; one originates from the spherical Fermi surface with effective mass of about 0.085 m(0), the other from the layered structure spread in the a-b plane. In the case of Si-doped InN with the carrier density of 2.5 x 10(18) cm(-3), about half electron density exists on the a-b plane. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

    DOI: 10.1002/pssc.200303461

  • High-quality InN film grown on a low-temperature-grown GaN intermediate layer by plasma-assisted molecular-beam epitaxy Reviewed

    M Higashiwaki, T Matsui

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS   41 ( 5B )   L540 - L542   2002.05( ISSN:0021-4922

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    High-quality indium nitride (InN) films were grown on sapphire substrates by plasma-assisted molecular-beam epitaxy. The structural and electrical properties of the InN films were greatly improved by employing a buffer layer formed with a low-temperature-grown GaN intermediate layer and a low-temperature-grown InN layer. The surface morphology of the InN film was quite smooth - the root-mean-square roughness was less than 5 run. The room-temperature Hall mobility was 1180 cm(2)/V.s, and the residual electron concentration was 1.6 x 10(18) cm(-3). These results indicate that the InN film almost meets the requirements for application to practical devices.

    DOI: 10.1143/JJAP.41.L540

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  • Fabrication technology and device performance of sub-50-nm-gate InP-based high electron mobility transistors Reviewed

    A Endoh, Y Yamashita, K Shinohara, M Higashiwaki, K Hikosaka, T Mimura, S Hiyamizu, T Matsui

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS   41 ( 2B )   1094 - 1098   2002.02( ISSN:0021-4922

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    We fabricated sub-50-nm-gate InAlAs/InGaAs high electron mobility transistors (HEMTs) lattice-matched to InP substrates. The two-step-recessed gate technology and low-temperature process, with all steps taking place below 300degreesC, allowed us to fabricate sub-50-nm-gate HEMTs that had high levels of performance. We succeeded in fabricating ultrashort 25-nm-long T-shaped gates. DC measurements showed that the 25-nm-gate HEMT had good pinchoff behavior, and that its maximum transconductance g(m) was about 770 mS/mm. A cutoff frequency f(T) of 396 GHz was obtained for the 25-nm-gate HEMT. This f(T) is the highest value yet reported for a transistor of any type, and the gate length of 25 nm is the shortest value ever reported for any compound semiconductor transistor that exhibits true device operation.

    DOI: 10.1143/JJAP.41.1094

    CiNii Article

  • Plasma-assisted MBE growth of InN film and InAlN/InN heterostructure Reviewed

    M. Higashiwaki, T. Matsui

    MBE 2002 - 2002 12th International Conference on Molecular Beam Epitaxy   235 - 236   2002

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    InN has not been studied so much among III-nitride compound semiconductors, even though it is an attractive material from the viewpoint of practical device application. Theoretical studies have predicted that its saturation and overshoot electron velocities in InN film would be the highest among nitride compounds and that InN-based transistors would be extremely fast and have a cutoff frequency of over 1 THz. However, InN epitaxial film and InN-based heterostructures with quality sufficient for practical device application have not been obtained due to difficulties with InN epitaxial growth, such as a low dissociation temperature and the lack of a suitable lattice-matched substrate. We have reported that a buffer layer formed with a low-temperature-grown GaN (LT-GaN) intermediate layer and a LT-InN layer on a sapphire substrate improves electrical and structural properties of InN epitaxial film. The highest Hall mobility and lowest carrier density of our plasma-assisted MBE-grown InN film at room temperature were 1420 cm2/V·s and 1.4×1018 cm-3, respectively. In this summary, we report on plasma-assisted MBE growth of InN thin film and of an InAlN/InN heterostructure on a sapphire substrate.

    DOI: 10.1109/MBE.2002.1037846

  • Effect of low-temperature-grown GaN intermediate layer on InN growth by plasma-assisted MBE Reviewed

    M Higashiwaki, T Matsui

    INTERNATIONAL WORKSHOP ON NITRIDE SEMICONDUCTORS, PROCEEDINGS   0 ( 1 )   360 - 363   2002

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    We found that inserting a low-temperature-grown layer of GaN between a low-temperature-grown InN buffer layer and a sapphire substrate was an effective way of improving structural and electrical properties of InN films grown by plasma-assisted molecular beam epitaxy. The surface of a 260 nm thick InN film grown under the optimum condition was smooth, with a surface root-mean-square roughness of less than 4 nm. The Hall mobility of the InN film at room temperature was greater than 1500 cm(2)/Vs with an electron density of less than 2.0 x 10(18) cm(-3).

    DOI: 10.1002/pssc.200390063

  • High RF performance of 50-nm-gate lattice-matched InAlAs/InGaAs HEMTs Reviewed

    A Endoh, Y Yamashita, M Higashiwaki, K Hikosaka, T Mimura, S Hiyamizu, A Matsui

    IEICE TRANSACTIONS ON ELECTRONICS   E84C ( 10 )   1328 - 1334   2001.10( ISSN:0916-8524

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    We fabricated 50-nm-gate InAlAs/InGaAs high electron mobility transistors (HEMTs) lattice-matched to InP substrates by using a conventional process under low temperatures, below 300 degreesC, to prevent fluorine contamination and suppress possible diffusion of the Si-delta -doped sheet in the electron-supply layer, and measured the DC and RF performance of the transistors. The DC measurement showed that the maximum transconductance g(m) of a 50-nm-gate HEMT is about 0.91 S/mm. The cutoff frequency f(T) of our 50-nm-gate HEMT is 362 GHz, which is much higher than the values reported for previous 50-nm-gate lattice-matched HEMTs. The excellent RF performance of our HEMTs results from a shortening of the lateral extended range of charge control by the drain field, and this may have been achieved because the low-temperature fabrication process suppressed degradation of epitaxial structure.

  • Ultra-short 25-nm-gate lattice-matched InAlAs/InGaAs HEMTs within the range of 400 GHz cutoff frequency Reviewed

    Y Yamashita, A Endoh, K Shinohara, M Higashiwaki, K Hikosaka, T Mimura, S Hiyamizu, T Matsui

    IEEE ELECTRON DEVICE LETTERS   22 ( 8 )   367 - 369   2001.08( ISSN:0741-3106

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    We have succeeded in fabricating ultra-short 25-nm-gate InAlAs/InGaAs high electron mobility transistors (HEMTs) lattice-matched to InP substrates, The two-step-recessed gate technology and low temperature processing at below 300 degreesC allowed the fabrication of such ultra-short gates. DC measurements showed that the 25-nm-gate HEMT had good pinchoff behavior. We obtained a cutoff frequency f(T) of 396 GHz, within the range of 400 GHz f(T), for the 25-nm-gate HEMT. This f(T) is the highest value yet reported for any type of transistor, and the gate length of 25 mm is the shortest value ever reported for any compound semiconductor transistor that exhibits device operation.

    DOI: 10.1109/55.936345

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  • Research project on millimeter-wave semiconductor devices

    Matsui, T., Shinohara, K., Higashiwaki, M., Hirose, N.

    Journal of the Communications Research Laboratory   48 ( 4 )   2001

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  • Fabrication technology and device performance of sub-50-nm-gate InP-based HEMTs Reviewed

    A Endoh, Y Yamashita, K Shinohara, M Higashiwaki, K Hikosaka, T Mimura, S Hiyamizu, T Matsui

    2001 INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS, CONFERENCE PROCEEDINGS   448 - 451   2001( ISSN:1092-8669

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    Sub-50-nm-gate InAlAs/InGaAs high electron mobility transistors (HEMTs) lattice-matched to InP substrates were fabricated. Our method of fabrication includes the two-step-recess gate technology and a low temperature process, applied at below 300 degreesC. We succeeded in fabricating ultra-short 25-nm-long T-shaped-gates. RF measurements showed that the cutoff frequency f(T), of a 25-nm-gate HEMT is 396 GHz, and this is the highest value yet reported for any type of transistor.

    DOI: 10.1109/ICIPRM.2001.929171

  • Laser operation at room temperature of self-organized in0.1Ga0.9As/(GaAs)6(AlAs)1 quantum wires grown on (775)B-oriented GaAs substrates by molecular beam epitaxy

    Yasuhide Ohno, Masataka Higashiwaki, Satoshi Shimomura, Satoshi Hiyamizu, Seiji Ikawa

    Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures   18 ( 3 )   1672 - 1674   2000.12( ISSN:1071-1023

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    In0.1Ga0.9As/(GaAs)6(AlAs)1 quantum wires (QWRs) were naturally formed in a 3.0-nm- or 4.8-nm-thick In0.1Ga0.9As/(GaAs)6(AlAs)1 quantum well grown on a (775)B-oriented GaAs substrate by molecular beam epitaxy which has a corrugated AlAs-on-InGaAs upper interface (a period of about 40 nm and a vertical amplitude of about 2 nm) and a flat InGaAs-on-AlAs lower interface. Strong polarization dependence [P≡(I∥-I⊥)/(I∥+I ⊥) = 0.15] of photoluminescence spectrum from the (775)B InGaAs QWR structures (Lw = 3.0nm) was observed at 11 K, indicating their good one dimensionality. Graded index separate confinement heterostructure-type self-organized (775)B In0.1Ga0.9As/(GaAs)6(AlAs)1QWR lasers were fabricated, and they showed laser oscillation with threshold current densities of 1.7-3.1 kA/cm2 and lasing wavelengths of 833-868 nm at room temperature (27 °C) under pulsed current condition. © 2000 American Vacuum Society.

    DOI: 10.1116/1.591449

  • High f(T) 50-nm-gate InAlAs/InGaAs high electron mobility transistors lattice-matched to InP substrates Reviewed

    Y Yamashita, A Endoh, M Higashiwaki, K Hikosaka, T Mimura, S Hiyamizu, T Matsui

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS   39 ( 8B )   L838 - L840   2000.08( ISSN:0021-4922

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    We fabricated 50-nm-gate InAlAs/InGaAs high electron mobility transistors (HEMTs) lattice-matched to InP substrates using a conventional process under low temperatures below 300 degrees C, and measured DC and RF performance. nle measured cutoff frequency f(T) of our 50-nm-gate HEMT is 362 GHz, which is the highest value ever reported for any transistor, and is much higher than the values reported for previous 50-nm-gate lattice-matched HEMTs. The excellent RF performance of our HEMTs might result from the low-temperature fabrication process.

    DOI: 10.1143/jjap.39.L838

    CiNii Article

  • DC and RF performance of 50 nm gate pseudomorphic In0.7Ga0.3As/In0.52Al0.48As high electron mobility transistors grown on (411)A-oriented InP substrates by molecular-beam epitaxy Reviewed

    M Higashiwaki, T Kitada, T Aoki, S Shimomura, Y Yamashita, A Endoh, K Hikosaka, T Mimura, T Matsui, S Hiyamizu

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS   39 ( 7B )   L720 - L722   2000.07( ISSN:0021-4922

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    In this paper, we report on the material and device characteristics of pseudomorphic In0.7Ga0.3As/In0.52Al0.48As high electron mobility transistors (HEMTs) grown on a(411)A-oriented InP substrate by molecular-beam epitaxy. The electron Hall mobility in the (411)A HEMT was 2.5 times higher at 15K and 1.3 times higher even at room temperature than that in a HEMT grown on a conventional (100) InP substrate. The (411)A HEMTs with 50 nm gates provided excellent DC anti RF device characteristics. The maximum transconductance was as high as 1.1 S/mm, and the cutoff frequency reached 355 GHz.

    DOI: 10.1143/jjap.39.L720

    CiNii Article

  • Pseudomorphic In0.7Ga0.3As/In0.52Al0.48As HEMTs with super-flat interfaces fabricated on (411)A-oriented InP substrates Reviewed

    M Higashiwaki, T Kitada, T Aoki, S Shimomura, Y Yamashita, A Endoh, K Hikosaka, T Mimura, T Matsui, S Hiyamizu

    2000 INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS, CONFERENCE PROCEEDINGS   573 - 576   2000( ISSN:1092-8669

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    In this paper, we report the device fabrication and characteristics of 50-nm-gate pseudomorphic In0.7Ga0.3As/In0.52Al0.48As high electron mobility transistors (HEMTs) grown on a (411) A-oriented InP substrate by molecular beam epitaxy, which is the first report, to our knowledge, of HEMTs grown on any InP substrate except a conventional (100)-oriented InP substrate. The pseudomorphic HEMTs on the (411) A InP substrate showed a higher electron mobility than those on the (100) InP substrate at not only low temperatures but also room temperature. The (411) A HEMTs provided excellent DC and RF characteristics, showing a very high transconductance (1.1 S/mm) and one of the best cutoff frequencies (355 GHz) ever reported.

    DOI: 10.1109/ICIPRM.2000.850362

  • Laser operation at room temperature of self-organized In0.1Ga0.9As/(GaAs)6(AlAs)1 quantum wires grown on (775)B-oriented GaAs substrates by molecular beam epitaxy Reviewed

    Y. Ohno, M. Higashiwaki, S. Shimomura, S. Hiyamizu, S. Ikawa

    J. Vac. Sci. Tech. B   18 ( 3 )   1672 - 1674   2000( ISSN:0734-211X

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    DOI: 10.1116/1.591449

    CiNii Article

  • High f(T) 50-nm-gate lattice-matched InAlAs/InGaAs HEMTs Reviewed

    A Endoh, Y Yamashita, M Higashiwaki, K Hikosaka, T Mimura, S Hiyamizu, T Matsui

    2000 INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS, CONFERENCE PROCEEDINGS   87 - 90   2000( ISSN:1092-8669

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    Publishing type:Research paper (international conference proceedings)  

    We fabricated 50-nm-gate lattice-matched InAlAs/InGaAs High Electron Mobility Transistors (HEMTs) using a conventional process under low temperatures below 300 degrees C, and measured DC and RF performance. The measured cutoff frequency f(T) of our 50-nm-gate HEMT is 362 GHz, which is much higher than those in previous works, and the highest value ever reported for any transistor. The excellent RF performance might result from the low-temperature fabrication process.

    DOI: 10.1109/ICIPRM.2000.850238

  • In0.15Ga0.85As/GaAs quantum wire structures grown on (553)B GaAs substrates by molecular beam epitaxy Reviewed

    S Hiyamizu, Y Ohno, M Higashiwaki, S Shimomura

    JOURNAL OF CRYSTAL GROWTH   201   824 - 827   1999.05( ISSN:0022-0248

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    Self-organized In0.15Ga0.85As quantum wires (QWRs) were formed in an In0.15Ga0.85As quantum well (QW) with GaAs barrier lavers grown on a (5 5 3)B-oriented GaAs substrate by molecular beam epitaxy. The QW has a regularly corrugated interface to the upper GaAs barrier (a lateral period of about 20 nm and a vertical amplitude of about 1.5 nm) and a rather flat interface to the lower GaAs barrier. A very narrow photoluminescence peak from the QWRs was observed at a wavelength of 864 nm at 15 K. The PL peak showed strong polarization dependence [the polarization degree P = (I-parallel to - I-perpendicular to)/(I-parallel to + I-perpendicular to) = 0.25] at 15 K, indicating high one dimensionality of the (5 5 3)B QWRs. The full-width at half-maximum (FWHM) of the PL peak was as small as 8.4 meV (15 K) which is, to our knowledge, the smallest PL-FWHM reported so far for self-organized QWRs. (C) 1999 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0022-0248(98)01449-3

  • GaAs/(GaAs)(4)(AlAs)(2) quantum wire lasers grown on (775)B-oriented GaAs substrates by molecular beam epitaxy Reviewed

    M Higashiwaki, S Ikawa, S Shimomura, S Hiyamizu

    JOURNAL OF CRYSTAL GROWTH   201   886 - 890   1999.05( ISSN:0022-0248

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    Stripe-geometry lasers with high-density GaAs/(GaAs)(4) (AlAs)(2) quantum wires (QWRs) as an active region were grown on (7 7 5)B-oriented GaAs substrates by molecular beam epitaxy. The (7 7 5)B QWRs were naturally formed at thick parts in a GaAs/(GaAs)(4) (AlAs)(2) quantum well with a corrugated A1As-on-GaAs upper interface and a Aat GaAs-on-AlAs lower interface. The (7 7 5)B QWR lasers with a high one-dimensionality exhibited threshold current densities of 1.9 kA/cm(2) at 20 degrees C for a cavity length of 1 mm, which were about 35% lower than those of conventional QW lasers simultaneously grown on (1 0 0) GaAs substrates. Moreover, they showed a 30% higher characteristic temperature in the range of 20-80 degrees C than the (1 0 0) QW lasers. (C) 1999 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0022-0248(98)01492-4

    CiNii Article

  • Self-organized GaAs quantum-wire lasers grown on (775) B-oriented GaAs substrates by molecular beam epitaxy Reviewed

    M Higashiwaki, S Shimomura, S Hiyamizu, S Ikawa

    APPLIED PHYSICS LETTERS   74 ( 6 )   780 - 782   1999.02( ISSN:0003-6951

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    Self-organized GaAs/(GaAs)(4)(AlAs)(2) quantum-wire (QWR) lasers were grown on (775) B-oriented GaAs substrates by molecular-beam epitaxy. The QWRs were naturally formed at thick parts in the GaAs/(GaAs)(4)(AlAs)(2) quantum well with a corrugated AlAs-on-GaAs upper interface and a flat GaAs-on-AlAs lower interface. The density of the QWRs was as high as 8 X 10(6) cm(-1). Stripe-geometry lasers with the self-organized (775) B GaAs/(GaAs)(4)(AlAs)(2) QWRs as an active region oscillated at 20 degrees C with threshold current densities of about 3 kA/cm(2) for uncoated mirrors. (C) 1999 American Institute of Physics. [S0003-6951(99)01806-9].

    DOI: 10.1063/1.123365

    CiNii Article

  • Higher mobility with high concentration of 2DEG in pseudomorphic In0.7Ga0.3As/In0.52Al0.48As quantum-well HEMT structure with (411)A super-flat interfaces grown on (411)A InP substrate by MBE

    S. Hiyamizu, T. Kitada, T. Aoki, M. Higashiwaki, S. Shimomura

    Conference Proceedings - International Conference on Indium Phosphide and Related Materials   24 - 25   1999.01( ISSN:1092-8669

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    A high-quality pseudomorphic In0.7Ga0.3As/In0.52Al0.48As quantum-well (QW)-HEMT structure grown on (411)A InP substrates by molecular beam epitaxy (MBE) shows the highest mobility (39,700 cm2/Vs at 77 K) of two-dimensional electron gas (2DEG). The pseudomorphic In0.7Ga0.3As/In0.52Al0.48As QW-HEMT structures consisted of, from the top, a Si-doped InGaAs contact layer (40 nm thick), an In0.52Al0.48As layer (20 nm), a Si-sheet-doped In0.52Al0.48As layer (20 nm) with a nominal doping concentration of 1×1013 cm-2, an In0.52Al0.48As spacer layer (3 nm), a pseudomorphic In0.7Ga0.3As QW channel layer (12 nm), an In0.52Al0.48As layer (300 nm) and an In0.53Ga0.47As buffer layer (25 nm). The high-mobility (411)A sample can be expected to improve high-speed performance of InGaAs/InAlAs HEMTs.

  • Self-organized quantum wire lasers grown on (775)B-oriented GaAs substrates

    M. Higashiwaki

    Compound Semiconductor   5 ( 6 )   38 - 39   1999

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  • High-density In0.14Ga0.86As/(GaAs)(5)(AlAs)(5) quantum wires naturally formed on (775)B-oriented GaAs substrates by molecular beam epitaxy Reviewed

    S Hiyamizu, M Higashiwaki, M Yamamoto, S Shimomura

    MICROELECTRONIC ENGINEERING   43-4   335 - 340   1998.08( ISSN:0167-9317

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    In0.14Ga0.86As/(GaAs)(5)(AlAs)(5) Quantum Wires (QWRs) were naturally formed in a thin In0.14Ga0.86As/(GaAs)(5)(AlAs)(5) Quantum Well (QW) with a regularly corrugated AlAs/In0.14Ga0.86As upper interface (a period of about 40 nm) and a flat In0.14Ga0.86As/AlAs lower interface grown on (775)B-oriented GaAs substrates by molecular beam epitaxy. The QWRs were formed side by side with a high density of 2.5 x 10(5) QWRs cm(-1). A photoluminescence from the QWRs formed in the QW with an average well width of 2.2 nm, which have a cross section of about 40 x 4 nm(2), showed a strong polarization dependence [the polarization degree P = (I-parallel to - I-perpendicular to)/(I-parallel to + I-perpendicular to) = 0.19], indicating good one-dimensionality of those QWRs. Full width at half maximum of the PL peak from the In0.14Ga0.86As/(GaAs)(5)(AlAs)5 QWRs was as small as 17 meV at 14 K, which is smaller than any of other naturally synthesized QWRs reported so far. (C) 1998 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0167-9317(98)00182-8

  • Temperature dependence of exciton lifetimes in high-density GaAs/(GaAs)(4)(AlAs)(2) quantum wires grown on (775)B-oriented GaAs substrates by molecular beam epitaxy Reviewed

    M Higashiwaki, K Kuroyanagi, K Fujita, N Egami, S Shimomura, S Hiyamizu

    SOLID-STATE ELECTRONICS   42 ( 7-8 )   1581 - 1585   1998.07( ISSN:0038-1101

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    Photoluminescence (PL) decay time and its temperature dependence were studied in high-density GaAs/(GaAs)(4)(AlAs)(2) quantum wires (QWRs) grown on a (775)B GaAs substrate by molecular beam epitaxy, which are naturally formed in a 2.1 nm-wide GaAs/(GaAs)(4)(AlAs)(2) quantum well (QW) with a corrugated upper AlAs/GaAs interface (a lateral period of 12 nm and a vertical amplitude of 1.2 nm) and a flat lower GaAs/AlAs interface. The PL decay rime of the (775)B QWRs (tau(QWR)) was 430 ps at 18 K, which is about 20% longer than that (tau(QW =) 360 ps) of a GaAs/(GaAs)(4)(AlAs)(2) QW simultaneously grown on a (100) GaAs substrate. tau(QWR) increased slowly with increasing temperature (T) as tau(QWR) = 30T(1/2) + 290 (PS), while tau(QW) varied as tau(QW) = 6T + 240 (ps). As a result, tau(QWR) became shorter than tau(QW) at 50 K. The PL decay time of the (775)B QWRs becomes longer again than that of the (100) QW in the rage of 70-80 K. These results suggest good one-dimensional characteristics of the (775)B QWRs. (C) 1998 Elsevier Science Ltd. All rights reserved.

    DOI: 10.1016/S0038-1101(98)00075-6

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  • Temperature dependence of photoluminescence from high-density GaAs/(GaAs)(4)(AlAs)(2) quantum wires grown on (775)B-oriented GaAs substrates by molecular beam epitaxy Reviewed

    M Higashiwaki, S Shimomura, S Hiyamizu

    PHYSICA E   2 ( 1-4 )   959 - 963   1998.07( ISSN:1386-9477

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    Temperature dependence of photoluminescence (PL) was investigated for high-density and highly uniform GaAs/(GaAs)(4) (AlAs)(2) quantum wires (QWRs) grown on a (7 7 5)B GaAs substrate by molecular beam epitaxy, which are naturally formed in an average 2.1 nm width GaAs/(GaAs)(4)(AlAs)(2) quantum well (QW) with a corrugated upper interface (a lateral period of 12 nm and a vertical amplitude of 1.2 nm) and a flat lower interface. As temperature increases in the range of T greater than or equal to 60 K, PL intensity of the (7 7 5)B GaAs/(GaAs)(4)(AlAs)(2) QWRs decreases more slowly and is several times larger compared with that of a GaAs/(GaAs)4(A1As)z QW simultaneously grown on a (1 0 0) GaAs substrate, indicating reduction of the nonradiative decay process of exicitons in the (7 7 5)B QWRs. The full width at half maximum of the PL peak from the (7 7 5)B QWRs is almost independent of temperature above 60 K, while that of the (1 0 0) QW increases in proportion to about k(B)T above 50 K. These results strongly indicate the one-dimensional characteristics of the (7 7 5)B QWRs as theoretically predicted. (C) 1998 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S1386-9477(98)00197-0

    CiNii Article

  • Surface corrugation of GaAs layers grown on (775)B-oriented GaAs substrates by molecular beam epitaxy Reviewed

    M Yamamoto, M Higashiwaki, S Shimomura, N Sano, S Hiyamizu

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS   36 ( 10 )   6285 - 6289   1997.10( ISSN:0021-4922

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    Surface morphologies of GaAs layers grown on (775)B-oriented GaAs substrates by molecular beam epitaxy were studied using atomic force microscopy. The surface of a GaAs layer grown on a (775)B GaAs substrate is flat when it is grown at a substrate temperature (T-s) below 580 degrees C, but corrugates regularly for T-s' greater than or equal to 640 degrees C. Similar periodic corrugation of the (775)B GaAs surface formed during thermal annealing at T-s = 640 degrees C under As-4 atmosphere (10(-6) Torr), which is similar in shape to that of a GaAs layer in the early stage of growth (a GaAs layer thinner than 5 nm). As the thickness of a GaAs layer increases from 5 nm, the lateral period and step height of the corrugation increase and tend to saturate for thick GaAs layers (200 nm thick or more). The precise structure of the surface corrugation of a 3-nm-thick GaAs layer (the lateral period of 12 nm and step height of 1.2 nm) was observed as a corrugated AlAs-on-GaAs interface of a GaAs/(GaAs)(5)(AlAs)(5) quantum well structure with an average well width of 3 nm by cross-sectional transmission electron microscopy observation.

    DOI: 10.1143/JJAP.36.6285

    CiNii Article

  • Highly uniform and high-density GaAs/(GaAs)(4)(AlAs)(2) quantum wires grown on (775)B-oriented GaAs substrates by molecular beam epitaxy Reviewed

    M Higashiwaki, M Yamamoto, S Shimomura, S Hiyamizu

    APPLIED PHYSICS LETTERS   71 ( 14 )   2005 - 2007   1997.10( ISSN:0003-6951

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    Extremely uniform and high-density GaAs/(GaAs)(4)(AlAs)(2) quantum wires (QWRs) were self-organized in a thin GaAs/(GaAs)(4)(AlAs)(2) quantum well grown on a (775)B GaAs substrate with a regularly corrugated AlAs-on-GaAs interface and a flat GaAs-on-AlAs interface by molecular beam epitaxy. A strong photoluminescence (PL) peak at lambda=692 nm from the GaAs/ (GaAs)(4)(AlAs)(2) QWRs showed large polarization anisotropy [P = (I-parallel to - I-perpendicular to)/(I-parallel to + I-perpendicular to) = 0.19]. A full width at half-maximum of the PL peak from the QWRs was as small as 15 meV at 14 K, which is smaller than those of any self-organized GaAs/AlGaAs QWRs reported so far. Density of the QWRs (8 x 10(5) QWRs/cm) is the same as the highest ever reported. These results indicate that the QWRs grown on the (775)B GaAs. substrate meet requirements for applications to QWR lasers (high uniformity, high density, high optical quality, and simple fabrication process). (C) 1997 American Institute of Physics.

    DOI: 10.1063/1.119769

    CiNii Article

  • High-density GaAs/(GaAs)(2)(AlAs)(2) quantum wires naturally formed on (775)B-oriented GaAs substrates by molecular beam epitaxy Reviewed

    M Higashiwaki, M Yamamoto, S Shimomura, A Adachi, S Hiyamizu

    JOURNAL OF CRYSTAL GROWTH   175   814 - 818   1997.05( ISSN:0022-0248

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    GaAs/(GaAs)(2)(AlAs)(2) quantum wires (QWRs) were naturally firmed in a thin GaAs/(GaAs)(2)(AlAs)(2) quantum well (QW) with a regularly corrugated AlAs/GaAs upper interface (a period of 12 nm) and a flat GaAs/AlAs lower interface grown on (7 7 5)B-orienred GNAs substrates by molecular beam epitaxy. The QWRs were formed side by side with an extremely high density elf 8 x 10(5) QWRs/cm, which is the same to that of the previous GaAs/AlAs QWRs grown on the (7 7 5)B substrate (the highest density of QWRs ever reported [8]). A photoluminescence from the QWRs formed in the QW with an average well width (L-w) of 2.1 nm, which have a cross section of about 12 x 2 nm(2), showed a strong polarization dependence (the polarization degree P drop [(I parallel to - I perpendicular to)/(I parallel to + I perpendicular to)] = 0.21). The polarization degree is about twice as large as that of the precious GaAs/AlAs QWRs with an average L-w of 3.3 nm grown on the (7 7 5)B substrate. This improvement of the polarization degree is mainly due to the further reduced QW width, which results in an improved one-dimensional confinement of carriers in the present QWRs.

    DOI: 10.1016/S0022-0248(96)00861-5

  • High-density GaAs/AlAs quantum wires grown on (775)B-oriented GaAs substrates by molecular beam epitaxy Reviewed

    M Higashiwaki, M Yamamoto, T Higuchi, S Shimomura, SA Adachi, Y Okamoto, N Sano, S Hiyamizu

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS   35 ( 5B )   L606 - L608   1996.05( ISSN:0021-4922

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    GaAs/AlAs quantum wires (QWRs) were found to be naturally formed by a regularly corrugated AlAs/GaAs interface and a flat GaAs/AlAs interface in an AlAs/GaAs/AlAs quantum well with a well width of 3.3 nm grown on a (775)B GaAs substrate by molecular beam epitaxy. The lateral period and vertical amplitude of the AlAs/GaAs interface corrugation were 12 nm and 1.2 nm, respectively. The QWRs were formed side by side with an extremely high density of 8x10(5) QWRs/cm. A photoluminescence peak at lambda = 715 nm from the QWRs with a cross section of about 12x3 nm(2) showed a polarization degree of (I-parallel to - I-perpendicular to)/(I-parallel to + I-perpendicular to) = 0.11 and a very small full width at half maximum of 15 meV at 4.2 K.

    DOI: 10.1143/jjap.35.L606

    CiNii Article

  • LOW-TEMPERATURE ETCHING OF GAAS SUBSTRATES AND IMPROVED MORPHOLOGY OF GAAS GROWN BY METALORGANIC MOLECULAR-BEAM EPITAXY USING TRISDIMETHYLAMINOARSENIC AND TRIETHYLGALLIUM Reviewed

    D MARX, H ASAHI, XF LIU, M HIGASHIWAKI, AB VILLAFLOR, K MIKI, K YAMAMOTO, S GONDO, S SHIMOMURA, S HIYAMIZU

    JOURNAL OF CRYSTAL GROWTH   150 ( 1-4 )   551 - 556   1995.05( ISSN:0022-0248

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    Metalorganic molecular beam etching of a GaAs surface is observed at temperatures as low as 370 degrees C, for the first time, when the GaAs surface is exposed to TDMAAs (trisdimethylaminoarsenic) only. At this low temperature, not only the oxide layer is removed, but a smoothening of the surface also occurs. At higher temperatures (greater than or equal to 480 degrees C), however, this reaction of GaAs with TDMAAs is responsible for a roughening of the (100) GaAs surface, forming (411)A micro-facets. At low V/III beam pressure ratios (less than or equal to 0.5), smooth surfaces as well as good optical and electrical properties are obtained for GaAs layers grown even at high temperatures (550 less than or equal to T(sub)less than or equal to 650 degrees C). TDMAAs proves to be an extremely efficient arsenic source which can supply enough As even for a small V/III ratio of 0.25, and provides high GaAs growth-rates up to 2 mu m/h for a TDMAAs flux of 0.15 SCCM and TEG of 0.4 SCCM.

    DOI: 10.1016/0022-0248(94)00895-7

    CiNii Article

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Books and Other Publications

  • 次世代パワーエレクトロニクスの課題と評価技術

    東脇 正高( Role: Sole author ,  第1章「次世代パワーデバイスの動向と技術課題」、第3節「Ga2O3パワーデバイス」)

    S&T出版  2022.07 

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  • 次世代パワー半導体の開発・評価と実用化

    東脇 正高( Role: Contributor ,  第1編「次世代パワー半導体の開発」、第4章「Ga2O3 (酸化ガリウム) パワー半導体」、第1節「β型酸化ガリウムパワーデバイス開発」、pp. 185-192)

    エヌ・ティー・エス  2022.02  ( ISBN:4860437675

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    ASIN

  • Wide bandgap semiconductors for power electronics : materials, devices, applications

    M. Higashiwaki( Role: Contributor ,  Chapter 22 "Gallium Oxide: Material Properties and Devices", pp. 659-679)

    Wiley-VCH  2022.01  ( ISBN:3527346716

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    Total pages:736  

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  • 次世代パワー半導体の開発動向と応用展開

    東脇 正高( Role: Contributor ,  第2章「材料特性と開発」、第3節「酸化ガリウム材料・デバイス開発」、pp. 39-45)

    シーエムシー出版  2021.08  ( ISBN:9784781316130

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    Total pages:v,314p  

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  • Ultrawide bandgap semiconductors

    M. Higashiwaki( Role: Contributor ,  Chapter 1 "Fundamental technologies for gallium oxide transistors", pp. 1-22)

    Elsevier  2021.07  ( ISBN:9780128228708

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    Total pages:xiv, 465 p.  

    CiNii Books

  • 次世代パワー半導体デバイス・実装技術の基礎-Siから新材料への新展開- (設計技術シリーズ89)

    東脇 正高( Role: Contributor ,  第4章「Ga2O3パワーデバイス」、pp. 165-200)

    科学情報出版株式会社  2021.01  ( ISBN:4904774957

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    Total pages:279  

    CiNii Books

    ASIN

  • Phonon properties: Phonon and free charge carrier properties in monoclinic-symmetry β-Ga<inf>2</inf>O<inf>3</inf>

    Schubert M.

    Springer Series in Materials Science  2020  ( ISSN:0933033X

  • Introduction

    Higashiwaki M.

    Springer Series in Materials Science  2020  ( ISSN:0933033X

  • Field-effect transistors 2: Ga<inf>2</inf>O<inf>3</inf> field-effect transistors for power switching and radiation-hard electronics

    Wong M.H.

    Springer Series in Materials Science  2020  ( ISSN:0933033X

  • Gallium oxide : materials properties, crystal growth, and devices International journal

    Higashiwaki, Masataka, Fujita, Shizuo( Role: Supervisor (editorial))

    Springer  2020  ( ISBN:9783030371524

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    Total pages:xxviii, 764 p.   Book type:Scholarly book

    CiNii Books

  • Molecular beam epitaxy : materials and applications for electronics and optoelectronics

    M. Higashiwaki( Role: Contributor ,  Chapter 25 "MBE growth of Ga2O3 and its application", pp. 411-422)

    Wiley  2019.04  ( ISBN:111935501X

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    Total pages:512  

    CiNii Books

    ASIN

  • Gallium Oxide Field Effect Transistors - Establishing New Frontiers of Power Switching and Radiation-Hard Electronics

    Wong M.H.

    Wide Bandgap Semiconductor Electronics and Devices  2019.01  ( ISBN:9789811216480

  • MBE growth and device applications of Ga<inf>2</inf>O<inf>3</inf>

    Higashiwaki M.

    Molecular Beam Epitaxy: Materials and Applications for Electronics and Optoelectronics  2019.01  ( ISBN:9781119355021

  • 科学立国日本を築く : 極限に挑む気鋭の研究者たち II

    東脇 正高( Role: Contributor ,  第1章「LSI技術・電子デバイスの新展開」、第7節「超高周波窒化ガリウム (GaN) トランジスタ ~ミリ波帯超高速無線通信に向けて~」、pp. 49-56)

    日刊工業新聞社  2017.03  ( ISBN:4526056359

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    Total pages:冊  

    CiNii Books

  • 次世代パワー半導体の高性能化とその産業展開

    東脇 正高( Role: Contributor ,  第2編「材料開発」、第6章「酸化ガリウム:材料、デバイス開発」、pp. 47-55)

    シーエムシー出版  2015.06  ( ISBN:9784781310763

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    Total pages:vii, 251p  

    CiNii Books

  • ワイドギャップ半導体 あけぼのから最前線へ

    ( Role: Contributor ,  第2編「ワイドギャップ半導体エコ技術の最前線」、第5章「情報・通信エコ技術」、第3節「超高速電子デバイス」、pp. 326-336;第5章「情報・通信エコ技術」、第4節「近未来情報・通信システムへの展開」、pp. 336-342)

    培風館  2013.01  ( ISBN:4563067873

  • 2013 化合物半導体技術大全

    東脇 正高( Role: Contributor ,  第2編「化合物半導体基板・デバイス技術」、第7章「その他の化合物半導体基板・応用デバイス」、第4節「Ga2O3基板・応用デバイス」、pp. 98-101)

    電子ジャーナル  2013.01 

  • 高周波半導体材料・デバイスの新展開

    東脇 正高( Role: Contributor ,  第II編「結晶成長技術」、第2章「III-N化合物成長技術」、2.「MBE技術」、高周波半導体材料・デバイスの新展開」;第III編「デバイス技術」、第2章「III族窒化物系デバイス」、1. 「HEMT超高周波」、高周波半導体材料・デバイスの新展開」)

    シーエムシー出版  2006.11  ( ISBN:4882315823

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    Total pages:vii, 266p  

    CiNii Books

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MISC

  • ベータ酸化ガリウムパワー半導体に関する研究開発の動向と課題 Invited International journal

    東脇 正高

    工業材料   71 ( 4 )   6 - 7   2023.07

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    Authorship:Lead author, Last author, Corresponding author   Publishing type:Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)   International / domestic magazine:Domestic journal  

  • 酸化ガリウムパワーデバイスの技術動向と応用展開 Invited International journal

    東脇 正高

    工業材料   70 ( 1 )   8 - 12   2022.01

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    Authorship:Lead author, Last author, Corresponding author   Publishing type:Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)   International / domestic magazine:Domestic journal  

  • 縦型酸化ガリウムパワーデバイスの開発動向 Invited International journal

    東脇 正高

    車載テクノロジー   8 ( 12 )   36 - 40   2021.12

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    Authorship:Lead author, Last author, Corresponding author   Publishing type:Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)   International / domestic magazine:Domestic journal  

  • ベータ酸化ガリウムデバイス Invited Reviewed International journal

    東脇 正高

    応用物理   90 ( 5 )   283 - 289   2021.05

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    Authorship:Lead author, Last author, Corresponding author   Publishing type:Article, review, commentary, editorial, etc. (scientific journal)   International / domestic magazine:Domestic journal  

  • 酸化ガリウム電子デバイス研究開発 Invited Reviewed International journal

    東脇 正高、上村 崇史

    情報通信研究機構研究報告   66 ( 1 )   67 - 73   2020.08

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    Authorship:Lead author, Corresponding author   Publishing type:Article, review, commentary, editorial, etc. (bulletin of university, research institution)   International / domestic magazine:Domestic journal  

  • 酸化ガリウムパワーデバイスの可能性 Invited International journal

    東脇 正高

    日本信頼性学会誌   42 ( 5 )   235 - 240   2020.05

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    Authorship:Lead author, Last author, Corresponding author   Publishing type:Article, review, commentary, editorial, etc. (scientific journal)   International / domestic magazine:Domestic journal  

  • 酸化ガリウムエレクトロニクス Invited International journal

    東脇 正高

    パリティ   33 ( 1 )   38 - 39   2018.01

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    Authorship:Lead author, Last author, Corresponding author   Publishing type:Article, review, commentary, editorial, etc. (scientific journal)   International / domestic magazine:Domestic journal  

  • 酸化ガリウムパワーデバイスの動向 Invited International journal

    東脇 正高

    月刊誌OHM   105   23 - 25   2018.01

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    Authorship:Lead author, Last author, Corresponding author   Publishing type:Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)   International / domestic magazine:Domestic journal  

  • 酸化ガリウムトランジスターの夜明け Invited International journal

    東脇 正高

    パリティ   32 ( 10 )   52 - 56   2017.10

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    Authorship:Lead author, Last author, Corresponding author   Publishing type:Article, review, commentary, editorial, etc. (scientific journal)   International / domestic magazine:Domestic journal  

  • HVPE法による高品質酸化ガリウムエピタキシャル成長技術

    熊谷 義直, 村上 尚, 倉又 朗人, 東脇 正高

    応用物理   86 ( 2 )   107 - 111   2017.02( ISSN:0369-8009

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  • エネルギーデバイス最前線 酸化ガリウムパワーデバイスの最新技術と実用化への課題

    東脇 正高, 熊谷 義直, 村上 尚, 倉又 朗人

    エネルギーデバイス = Energy device   3 ( 6 )   43 - 47   2016.08( ISSN:2188-1383

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  • Ga₂O₃上に堆積したSiO₂膜におけるポストアニールの影響 (電子デバイス)

    小西 敬太, 上村 崇史, ワン マンホイ, 佐々木 公平, 倉又 朗人, 山腰 茂伸, 東脇 正高

    電子情報通信学会技術研究報告 = IEICE technical report : 信学技報   116 ( 158 )   11 - 15   2016.07( ISSN:0913-5685

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  • 高耐圧ディスプレッション型フィールドプレートGa₂O₃ MOSFET (電子デバイス研究会 次世代化合物半導体デバイスの機能と応用)

    ワン マンホイ, 東脇 正高, 佐々木 公平, 倉又 朗人, 山腰 茂伸

    電気学会研究会資料. EDD = The papers of technical meeting on electron devices, IEE Japan   2016 ( 36 )   29 - 33   2016.03

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  • State-of-the-art technology on gallium oxide power devices

    東脇正高, WONG Man Hoi, 小西敬太, 佐々木公平, 佐々木公平, 後藤健, 後藤健, 野村一城, THIEU Quang Tu, 富樫理恵, 村上尚, 熊谷義直, MONEMAR Bo, 纐纈明伯, 倉又朗人, 増井建和, 山腰茂伸

    電子情報通信学会技術研究報告   115 ( 402(ED2015 112-120) )   13‐18   2016.01( ISSN:0913-5685

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  • Siドープ酸化ガリウム厚膜のHVPEホモエピタキシャル成長

    野村一城, 後藤健, 後藤健, 佐々木公平, 佐々木公平, THIEU Quang Tu, 富樫理恵, 村上尚, 東脇正高, 倉又朗人, 山腰茂伸, BO Monemar, BO Monemar, 纐纈明伯, 熊谷義直

    結晶成長国内会議予稿集(CD-ROM)   45th   ROMBUNNO.19PB08   2015.10( ISSN:0385-6275

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  • Optical and Electrical Device Application of Gallium Oxide Single Crystal

    倉又朗人, 飯塚和幸, 佐々木公平, 輿公祥, 増井建和, 森島嘉克, 後藤健, 熊谷義直, 村上尚, 纐纈明伯, WONG Man Hoi, 上村崇史, 東脇正高, 山腰茂伸

    日本結晶成長学会誌(CD-ROM)   42 ( 2 )   130 - 140   2015.07( ISSN:2188-7268

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  • Optical and Electrical Device Application of Gallium Oxide Single Crystal(<Special Issue>Recent Advance in Functional Single Crystals)

    Kuramata Akito, Koukitu Akinori, Wong Man Hoi, Kamimura Takafumi, Higashiwaki Masataka, Yamakoshi Shigenobu, Iizuka Kazuyuki, Sasaki Kohei, Koshi Kimiaki, Masui Takekazu, Morishima Yoshikatsu, Goto Ken, Kumagai Yoshinao, Murakami Hisashi

    Journal of the Japanese Association for Crystal Growth   42 ( 2 )   130 - 140   2015( ISSN:0385-6275

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    Gallium Oxide is attracting attention as a new material for optical and electrical applications. It has a large band gap of 4.8 eV. The electron concentration can be controlled in a range between 10^&lt;16&gt; cm^&lt;-3&gt; and 10^&lt;19&gt; cm^&lt;-3&gt;. Large-size bulk crystals can be obtained easily because melt growth is possible under the atmospheric pressure. From these material features, we expect high performance and low production cost of LEDs and high power devices. In this report, we introduce the properties of β-Ga_2O_3 single crystal substrates and the present status of device development.

    CiNii Article

  • Band Offset at Al_2O_3/β-Ga_2O_3 Heterojunctions

    KAMIMURA Takafumi, SASAKI Kohei, WONG Man Hoi, DAIVASIGAMANI Krishnamurthy, KURAMATA Akito, MASUI Takekazu, YAMAKOSHI Shigneobu, HIGASHIWAKI Masataka

    IEICE technical report. Electron devices   114 ( 168 )   41 - 46   2014.08( ISSN:0913-5685

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    The band alignment of Al_2O_3/n-Ga_2O_3 (010) was investigated by x-ray photoelectron spectroscopy (XPS). With a band gap of 6.8±0.2 eV measured for Al_2O_3, the conduction and valance band offsets at the interface were estimated to be 1.5±0.2 eV and 0.7±0.2 eV, respectively. The conduction band offset was also obtained from tunneling current in Au/Al_2O_3/n-Ga_2O_3 (2^^-01) metal-oxide-semiconductor (MOS) diodes using the Fowler-Nordheim model. The electrically extracted value was in good agreement with the XPS data. Furthermore, the MOS diodes exhibited small capacitance-voltage hysteresis loops, indicating the successful engineering of a high-quality Al_2O_3/Ga_2O_3 interface.

    CiNii Article

  • Depletion-mode gallium oxide metal-oxide-semiconductor field-effect transistors fabricated by using Si-ion implantation

    HIGASHIWAKI Masataka, SASAKI Kohei, WONG Man HOI, KAMIMURA Takafumi, KRISHNAMURTHY Daivasigamani, KURAMATA Akito, MASUI Takekazu, YAMAKOSHI Shigenobu

    IEICE technical report. Microwaves   113 ( 379 )   35 - 39   2014.01( ISSN:0913-5685

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    Depletion-mode gallium oxide (Ga_2O_3) MOSFETs were fabricated on single-crystal β-Ga_2O_3 (010) substrates. We applied Si-ion implantation to the ohmic contacts for low contact resistance as well as to the channel layer for reliable doping. An Al_2O_3 gate dielectric film formed by atomic layer deposition passivated the device surface and significantly reduced gate leakage. The MOSFETs with a simple structure exhibited complete channel pinch-off with a breakdown voltage of 415 V and a drain current on/off ratio of ten orders of magnitude at room temperature. The devices also showed stable operation up to 250℃.

    CiNii Article

  • Characterization of Al_2O_3/n-Ga_2O_3 MOS diodes

    KAMIMURA Takafumi, WONG MAN Hoi, SASAKI Kohei, DAIVASIGAMANI Krishnamurthy, KURAMATA Akito, MASUI Takekazu, YAMAKOSHI Shegenobu, HIGASHIWAKI Masataka

    IEICE technical report. Electron devices   113 ( 176 )   29 - 32   2013.08( ISSN:0913-5685

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    We have analyzed the structural and electrical properties of Al_2O_3/Ga_2O_3 MOS diodes fabricated on a Ga_2O_3 (010) substrate by using transmission electron microscopy and capacitance-voltage measurements. The formation of a characteristic polycrystalline γ-Al_2O_3 film of about 3-nm thick at the initial stage of deposition was observed. The capacitance-voltage characteristic showed hysteresis, and an interface state density of 1.0×10^<12> cm^<-2> at the Al_2O_3/Ga_2O_3 interface was extracted by the Terman method. These results suggest that the polycrystalline film contributes to the formation of interface states in the Al_2O_3/Ga_2O_3 system.

    CiNii Article

  • Gallium Oxide Transistors

    32 ( 12 )   27 - 33   2012.12( ISSN:0286-4835

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  • Pt/β-Ga_2O_3 Schottky Barrier Diodes Using Single-Crystal β-Ga_2O_3 Substrates

    SASAKI Kohei, HIGASHIWAKI Masataka, KURAMATA Akito, MASUI Takekazu, YAMAKOSHI Shigenobu

    IEICE technical report. Component parts and materials   112 ( 328 )   25 - 28   2012.11( ISSN:0913-5685

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    We fabricated gallium oxide (Ga_2O_3) Schottky barrier diodes using β-Ga_2O_3 (010) single crystal substrates produced by the floating zone. The crystal quality of the substrates was excellent; the X-ray diffraction rocking curve peak had a full width at half maximum of 32 arcsec, and the etch pit density was less than 1×10^4cm^<-2>. The devices exhibited good characteristics, such as an ideality factor close to the unity and a reasonably high reverse breakdown voltage of about 150V. The Schottky barrier height of the Pt/β-Ga_2O_3 interface was estimated to be 1.3-1.5eV.

    CiNii Article

  • Replacing SiC with Gallium Oxide to Achieve Cheaper and Higher-Performance Power Devices

    ( 1079 )   81 - 89   2012.04( ISSN:0385-1680

  • Small-signal and 30 GHz power characteristics of AlGaN/GaN heterostructure field-effect transistors with thin AlGaN barrier layers : Effects of AlGaN barrier thinning

    HIGASHIWAKI Masataka, PEI Yi, CHU Rongming, MISHRA Umesh K.

    IEICE technical report. Electron devices   111 ( 338 )   13 - 17   2011.12( ISSN:0913-5685

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    Short-gate AlGaN/GaN heterostructure field-effect transistors (HFETs) with extremely thin AlGaN barrier layers were fabricated and characterized from the viewpoint of millimeter-wave applications. The devices showed good DC and RF small-signal characteristics; however, the 30 GHz power characteristics were degraded. The dispersive behavior of the thin-barrier devices measured in pulse I V curves was different from the commonly observed one. We consider from these results that the unique dispersion of the thin-barrier HFETs was caused by the different charging path related to hot electrons accelerated in a high electric field region of a two-dimensional electron gas channel.

    CiNii Article

  • Effects of surface oxidation during device processing on surface barrier height of AlGaN/GaN HFETs

    HIGASHIWAKI Masataka, CHOWDHURY Srabanti, SWENSON Brian L., MISHRA Umesh K.

    IEICE technical report   110 ( 80 )   31 - 35   2010.06( ISSN:0913-5685

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    We investigated effects of surface oxidation by annealing during device process on AlGaN surface barrier height of AlGaN/GaN heterostructures by Hall measurement and x-ray photoelectron spectroscopy (XPS). From AlGaN thickness dependence of two-dimensional electron gas density and XPS analysis, a constant surface barrier height regardless of AlGaN thickness was obtained for the samples annealed at 800℃. On the other hand, the samples annealed at 400℃ showed a proportional increase in the height with the thickness. Moreover, XPS peak intensity related to Al-O bonding significantly increased after annealing at 800℃ regardless of atmosphere and saturated in a short time, even though it changed little after annealing at 400℃ compared with before annealing. We consider from the experimental results and their correlation that Al oxide structure formed on the AlGaN surface significantly affects energy distribution and density of surface donors.

    CiNii Article

  • Research and Development of Millimeter-Wave GaN Transistors

    HIGASHIWAKI Masataka, MIMURA Takashi, MATSUI Toshiaki

    IEICE technical report   106 ( 403 )   1 - 6   2006.12( ISSN:0913-5685

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    GaN heterostructure field-effect transistors (HFETs) are promising not only as high-power and high-breakdown-voltage devices but also as high-frequency ones, because the saturation electron velocity in GaN is relatively high. By using three characteristic techniques to improve high-frequency characteristics of GaN HFETs, which are (1) high-Al-composition and extremely thin barrier layers, (2) Cat-CVD SiN passivation, and (3) T-shaped short gates defined by electron-beam lithography, we have succeeded in suppressing short-channel effects in short-gate HFETs with a gate length of less than 0.1μm. Here, we report on device characteristics of short-gate AlGaN/GaN and InAlN/GaN HFETs, which are being developed for applications in the frequency range above 50GHz.

    CiNii Article

  • Short-gate AlGaN/GaN HFETs with extremely thin AlGaN barriers for millimeter-wave operations

    HIGASHIWAKI Masataka, ONOJIMA Norio, MATSUI Toshiaki

    IEICE technical report   105 ( 329 )   93 - 96   2005.10( ISSN:0913-5685

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    We have succeeded in suppressing short-channel effects by using high-Al-composition and extremely thin AlGaN barrier layers to improve high-frequency characteristics of sub-0.1-μm AlGaN/GaN heterostructure field-effect transistors (HFETs). The devices had maximum drain current densities of 1.1-1.2A/mm and peak extrinsic transconductances of 305-441mS/mm. The current-gain cutoff frequency (f_T) of 163GHz and maximum oscillation frequency (f_<max>) of 192GHz were obtained for the 8-nm-AlGaN-barrier devices with 0.06- and 0.08-μm-long gates, respectively.

    CiNii Article

  • Fabrication of AlGaN/GaN HEMT Micro Hall Sensors for High Temperature Operation

    NAKAMURA D., HIGASHIWAKI M., MATSUI T., SANDHU A.

    28   391 - 391   2004.09

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  • Fabrication and Improvement of Schottky Gate Contacts of Ultra-Short-Gate GaN-Based HEMTs

    ENDOH Akira, YAMASHITA Yoshimi, IKEDA Keiji, HIGASHIWAKI Masataka, HIKOSAKA Kohki, MATSUI Toshiaki, HIYAMIZU Satoshi, MIMURA Takashi

    IEICE technical report. Electron devices   103 ( 558 )   35 - 40   2004.01( ISSN:0913-5685

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    We fabricated ultra-short-gate AlGaN/GaN high electron mobility transistors (HEMTs) and improved Schottky gate contacts by thermal annealing. Using a 27-nm i-Al_<0.22>Ga_<0.78>N layer, we obtained the gate length L_g dependence of the cutoff frequency f_T for the HEMTs with a source-drain spacing L_<sd> of 2μm under a drain-source voltage V_<ds> of 3 V. The peak f_T was measured to be 102 GHz at L_g=35 nm. The highest f_T of 110 GHz was obtained by reducing L_<sd> from 2 to 1.5 μm and by increasing V_<ds> from 3 to 4V. Using a 10-nm i-Al_<0.25>Ga_<0.75>N layer, we fabricated 120-nm Ni/Pt/Au-gate and Mo/Pt/Au-gate HEMTs. Enhancement-mode operation was achieved by using Ni/Pt/Au-gate HEMTs with thermal annealing at 500℃ and Mo/Pt/Au-gate HEMTs without thermal annealing.

    CiNii Article

  • Epitaxial Growth of High-Quality InN Thin Film on Sapphire Substrates by RF-MBE : Effect of low-temperature-grown InN/GaN buffer layers

    HIGASHIWAKI Masataka, MATSUI Toshiaki

    Technical report of IEICE. LQE   102 ( 117 )   97 - 100   2002.06( ISSN:0913-5685

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    Studying InN epitaxial growth on a sapphire substrate by RF-MBE, we found that a buffer layer formed with a low-temperature-grown GaN intermediate layer and a low-temperature-grown InN layer on a sapphire substrate was very effective to improve the crystal quality and adhesiveness of InN film. The surface of a 260-nm-thick InN film was quite smooth with the RMS roughness of 3.8 nm. The room-temperature Hall mobility and carrier density of the InN film were 1420 cm^2/V・s and 1.4×10^18 cm^-3, respectively.

    CiNii Article

  • Ultra-short T-shaped gate fabrication technique for sub-millimeter-wave InP-HEMTs : Optimization of process conditions

    SHINOHARA Keisuke, HIROSE Nobumitsu, HIGASHIWAKI Masataka, MATSUI Toshiaki, YAMASHITA Yoshimi, HIKOSAKA Kouki, MIMURA Takashi, HIYAMIZU Satoshi

    IEICE technical report. Electron devices   100 ( 548 )   43 - 47   2001.01( ISSN:0913-5685

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    InP-based InGaAs/InAlAs high electron mobility transistors (HEMTs) are considered to be one of the most promising devices for millimeter-wave radio communications because of their superior high frequency and low-noise performances. This is due to high electron mobility, high saturation velocity, and high sheet carrier density obtained in this system. A shorter gate is also essential for ultra-high RF performances. In our previous work, RF performances have been significantly improved by reducing gate length (L_g) down to 50 nm using a simple lift-off process and a low temperature process. In this paper, we have developed a sub-50-nm T-shaped-gate fabrication technique using a conventional tri-layer resist system by optimizing electron beam (EB) lithography and reactive ion etching (RIE) conditions, demonstrating a cutoff frequency (f_T)as high as 318 GHz in a 35-nm-gate HEMT.

    CiNii Article

  • 5a-E-6 Time-resolved PL measurements of high-density GaAs QWRs grown on (775)B GaAs substrates by MBE

    Higashiwaki M., Shimomura S., Hiyamizu S., Kuroyanagi K., Fujita K., Egami N.

    Meeting abstracts of the Physical Society of Japan   52 ( 2 )   142 - 142   1997.09( ISSN:1342-8349

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  • 31a-R-12 Optical properties of self-organized high-density GaAs QWRs grown on (775)B GaAs substrates by MBE

    Higashiwaki M, Yamamoto M, Shimomura S, Hiyamizu S, Ito M, Ogawa M, Miyoshi T

    Meeting abstracts of the Physical Society of Japan   52 ( 1 )   234 - 234   1997.03( ISSN:1342-8349

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Presentations

  • ワイドギャップ半導体SBDの高周波整流特性 Domestic conference

    大野 泰夫、伊藤 弘子、平岡 知己、東脇 正高

    第71回応用物理学会春季学術講演会  2024.03 

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    Presentation type:Oral presentation (general)  

    Venue:東京都市大学 世田ヶ谷キャンパス  

  • 酸素反応性イオンエッチング、窒素ラジカル照射がGa2O3ショットキーバリアダイオードの温度依存電気的特性に与える影響 Domestic conference

    佐藤 翔太、峰山 滉正、WANG Zhenwei、東脇 正高

    第71回応用物理学会春季学術講演会  2024.03 

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    Presentation type:Oral presentation (general)  

    Venue:東京都市大学 世田ヶ谷キャンパス  

  • 減圧ホットウォールMOCVD 成長したノンドープGa2O3薄膜の電気的特性(2) Domestic conference

    稲嶌 仁、森原 淳、WANG Zhenwe、吉永 純也、佐藤 翔太、江口 輝生、熊谷 義直、東脇 正高

    第71回応用物理学会春季学術講演会  2024.03 

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    Presentation type:Oral presentation (general)  

    Venue:東京都市大学 世田ヶ谷キャンパス  

  • 減圧ホットウォールMOCVD 成長したノンドープGa2O3薄膜の電気的特性(1) Domestic conference

    森原 淳、稲嶌 仁、WANG Zhenwe、吉永 純也、佐藤 翔太、江口 輝生、熊谷 義直、東脇 正高

    第71回応用物理学会春季学術講演会  2024.03 

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    Presentation type:Oral presentation (general)  

    Venue:東京都市大学 世田ヶ谷キャンパス  

  • Ga2O3 (010) FinFETs with on-Axis (100) gate sidewalls Domestic conference

    Zhenwei Wang, Sandeep Kumar, Takafumi Kamimura, Hisashi Murakami

    2024.03 

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  • マイクロ波無線電力伝送応用に向けた高周波Ga2O3ショットキーバリアダイオードの構造設計 Domestic conference

    江口 輝生、末廣 雄大、Romualdo A. Ferreyra、大野 泰夫、東脇 正高

    第71回応用物理学会春季学術講演会  2024.03 

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    Presentation type:Oral presentation (general)  

    Venue:東京都市大学 世田ヶ谷キャンパス  

  • MBE法による(AlxGa1-x)2O3結晶成長の熱力学的検討 Domestic conference

    富樫 理恵、東脇 正高、熊谷 義直

    第71回応用物理学会春季学術講演会  2024.03 

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    Presentation type:Oral presentation (general)  

    Venue:東京都市大学 世田ヶ谷キャンパス  

  • Development of vertical Ga2O3 power devices and their processing technologies Invited International conference

    Masataka Higashiwaki, Zhenwei Wang, Sandeep Kumar, Shota Sato, Kohki Eguchi, Kura Nakaoka, Syoki Taniguchi, Hisashi Murakami, and Yoshinao Kumagai

    8th IEEE Electron Devices Technology and Manufacturing Conference (IEEE EDTM 2024)  2024.03  IEEE

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    Presentation type:Oral presentation (invited, special)  

    Venue:Bangalore, India  

  • Vertical Ga2O3 (010) FinFETs Invited International conference

    Masataka Higashiwaki, Zhenwei Wang, Sandeep Kumar, Takafumi Kamimura, Hisashi Murakami, and Yoshinao Kumagai

    59th Annual Workshop on Compound Semiconductor Materials and Devices (WOCSEMMAD 2024)  2024.02 

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    Presentation type:Oral presentation (invited, special)  

    Venue:Las Vegas, USA  

  • β-Ga2O3電子デバイス開発の進展 Invited Domestic conference

    東脇 正高、大槻 匠、上村 崇史、Zhenwei Wang、佐藤 翔太、江口 輝生、中岡 蔵、谷口 奨季、村上 尚、熊谷 義直

    学振R032委員会 第15回研究会  2024.01 

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    Presentation type:Oral presentation (invited, special)  

    Venue:四日市市地場産業振興センター、三重  

  • 窒素ラジカル照射処理を施したGa2O3表面構造の評価 Domestic conference

    谷口 奨季、中岡 蔵、東脇 正高

    応用物理学会 先進パワー半導体分科会 第10回講演会  2023.12 

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    Presentation type:Poster presentation  

  • 窒素ラジカル照射によるGa2O3 (100), (010) ショットキーバリアダイオード電気的特性の改善 Domestic conference

    江口 輝生、佐藤 翔太、Zhenwei Wang、東脇 正高

    応用物理学会 先進パワー半導体分科会 第10回講演会  2023.11 

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    Presentation type:Poster presentation  

    Venue:金沢、石川  

  • Ⅲ族酸化物半導体結晶成長の熱力学的検討 Domestic conference

    富樫 理恵、後藤 健、東脇 正高、熊谷 義直

    薄膜材料デバイス研究会 第20回研究集会  2023.11 

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    Presentation type:Oral presentation (invited, special)  

    Venue:龍谷大学 響都ホール、京都  

  • 酸化ガリウムデバイス技術の現状と今後 Domestic conference

    酸化ガリウムデバイス技術の現状と今後

    透明酸化物光・電子材料研究会 第6回研究会「新しい機能材料と潮流」  2023.10 

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    Presentation type:Oral presentation (invited, special)  

    Venue:東京大学 本郷キャンパス  

  • Investigation on effects of oxygen reactive ion etching and nitrogen radical irradiation on Ga2O3 (100) and (010) Schottky barrier diodes Domestic conference

    2023.10 

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  • Effect of nitrogen radical irradiation on Ga2O3 surface structures Domestic conference

    2023.10 

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    Presentation type:Oral presentation (general)  

  • 窒化ラジカルを照射したGa2O3表面の構造評価 Domestic conference

    谷口 奨季、中岡 蔵、東脇 正高

    第84回応用物理学会秋季学術講演会  2023.09 

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    Presentation type:Oral presentation (general)  

    Venue:熊本城ホール  

  • 窒素ラジカル照射がGa2O3ショットキーバリアダイオードの電気的特性に及ぼす影響 Domestic conference

    江口 輝生、佐藤 翔太、Zhenwei Wang、東脇 正高

    第84回応用物理学会秋季学術講演会  2023.09 

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    Presentation type:Oral presentation (general)  

    Venue:熊本城ホール  

  • ベータ型酸化ガリウムデバイスの開発動向とダイオード、トランジスタ応用への展望 Invited Domestic conference

    東脇 正高

    技術情報協会講演会セミナー「次世代パワーデバイスに向けたデバイス化技術と要素技術の展望」  2023.09 

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    Presentation type:Public lecture, seminar, tutorial, course, or other speech  

    Venue:オンライン  

  • Effects of oxygen reactive ion etching and nitrogen radical irradiation on electrical properties of Ga2O3 Schottky barrier diodes International conference

    Shota Sato, Kohki Eguchi, Zhenwei Wang, Takahiro Kitada, and Masataka Higashiwaki

    6th U.S. Workshop on Gallium Oxide (GOX 2023)  2023.08 

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    Presentation type:Oral presentation (general)  

    Venue:Buffalo, NY, USA  

  • Structural properties of Ga2O3 surfaces treated by nitrogen radical irradiation International conference

    Kura Nakaoka, Syoki Taniguchi, Takahiro Kitada, and Masataka Higashiwaki

    6th U.S. Workshop on Gallium Oxide (GOX 2023)  2023.08 

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    Presentation type:Poster presentation  

    Venue:Buffalo, NY, USA  

  • Modelling of impedance dispersion in lateral β-Ga2O3 MOSFETs due to parallel conductive Si-accumulation layer International coauthorship International conference

    Zequan Chen, Abhishek Mishra, Aditya K Bhat, Matthew D Smith, Michael J Uren, Sandeep Kumar, Masataka Higashiwaki, and Martin Kuball

    6th U.S. Workshop on Gallium Oxide (GOX 2023)  2023.08 

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    Presentation type:Oral presentation (general)  

    Venue:Buffalo, NY, USA  

  • 酸化ガリウムパワーデバイスの最新技術・研究開発動向と今後の展開 Invited Domestic conference

    東脇 正高

    R&D支援センターセミナー「酸化ガリウムパワーデバイスの最新技術・研究開発動向と今後の展開」  2023.08 

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    Presentation type:Public lecture, seminar, tutorial, course, or other speech  

    Venue:オンライン  

  • Improvement of Ga2O3 Schottky barrier diode characteristics by nitrogen radical treatment

    Zhenwei Wang, Sandeep Kumar, Takahiro Kitada, and Masataka Higashiwaki

    65th Electronic Materials Conference (EMC)  2023.06 

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    Presentation type:Oral presentation (general)  

    Venue:Santa Barbara, CA, USA  

  • Application of (AlxGa1-x)2O3 as back barrier in lateral Ga2O3 radio-frequency field-effect transistors International conference

    Takumi Ohtsuki, Takafumi Kamimura, and Masataka Higashiwaki

    65th Electronic Materials Conference (EMC)  2023.06 

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    Presentation type:Oral presentation (general)  

    Venue:Santa Barbara, CA, USA  

  • Advances and prospects of gallium oxide material and device technologies Invited International conference

    Masataka Higashiwaki

    51st International School & Conference on the Physics of Semiconductors (Jaszowiec 2023)  2023.06 

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    Presentation type:Oral presentation (invited, special)  

    Venue:Szczyrk, Poland  

  • 酸化ガリウム: 材料・デバイス技術の現在地 Domestic conference

    東脇 正高

    第15回ナノ構造・エピタキシャル成長講演会  2023.06 

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    Presentation type:Oral presentation (invited, special)  

    Venue:山形テルサ、山形  

  • HVPE法による縦型Ga2O3デバイス用高純度高速エピ成長 Domestic conference

    熊谷 義直、後藤 健、村上 尚、佐々木 公平、倉又 朗人、東脇 正高

    応用電子物性分科会/結晶工学分科会 合同研究会「次世代ワイドギャップパワーデバイスの最前線」  2023.06 

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    Presentation type:Oral presentation (invited, special)  

    Venue:ウインクあいち、名古屋、愛知  

  • ベータ酸化ガリウムデバイス開発の最近の進展 Invited Domestic conference

    東脇 正高、上村 崇史、大槻 匠、Sandeep Kumar、Zhenwei Wang、江口 輝生、佐藤 翔太、谷口 奨季、中岡 蔵、村上 尚、熊谷 義直

    応用電子物性分科会/結晶工学分科会 合同研究会「次世代ワイドギャップパワーデバイスの最前線」  2023.06 

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    Presentation type:Oral presentation (invited, special)  

    Venue:ウインクあいち、名古屋、愛知  

  • Ion implantation doping technology for Ga2O3 and its application to device fabrication Invited International conference

    Masataka Higashiwaki, Ken Goto, Hisashi Murakami, and Yoshinao Kumagai

    21st International Workshop on Junction Technology (IWJT2023)  2023.06 

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    Presentation type:Oral presentation (invited, special)  

    Venue:Kyoto, Japan  

  • Sub-bandgap transition in β-Ga2O3 crystals measured by photoluminescence excitation spectroscopy International conference

    Takeyoshi Onuma, Ryuta Adachi, Kohei Shoji, Tomohiro Yamaguchi, Kohei Sasaki, Akito Kuramata, Tohru Honda, and Masataka Higashiwaki

    Compound Semiconductor Week 2023 (CSW 20223)  2023.06 

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    Presentation type:Poster presentation  

    Venue:Jeju, Korea  

  • 酸化ガリウムパワー半導体の特性と実用化への展望 Invited Domestic conference

    東脇 正高

    シーエムシー出版セミナー「次世代パワー半導体の高性能化と開発動向」  2023.05  シーエムシー出版

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    Presentation type:Public lecture, seminar, tutorial, course, or other speech  

    Venue:神田、東京  

  • Current status of gallium oxide material and device technologies Invited International conference

    M. Higashiwaki

    35th International Conference on Microelectronic Test Structures (ICMTS-35)  2023.03 

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    Presentation type:Oral presentation (invited, special)  

    Venue:Tokyo, Japan  

  • (AlxGa1-x)2O3バックバリアを用いた横型Ga2O3 MOSFETの高周波特性 Domestic conference

    大槻 匠、上村 崇史、東脇 正高

    第70回応用物理学会春季学術講演会  2023.03  応用物理学会

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    Venue:上智大 四ツ谷キャンパス、四ツ谷、東京  

  • Improvement in electrical properties of Ga2O3 Schottky barrier diodes by nitrogen radical treatment Domestic conference

    Zhenwei Wang, Takahiro Kitada, Sandeep Kumar, and Masataka Higashiwaki

    The 70th JSAP Spring Meeting  2023.03 

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  • 極限環境化での動作が可能な酸化ガリウムデバイス Invited Domestic conference

    上村 崇史、東脇 正高

    2023年 電子情報通信学会総合大会「BI-5 極限環境コミュニケーション 〜 こんなところに通信技術!?」  2023.03  電子情報通信学会

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    Presentation type:Oral presentation (invited, special)  

    Venue:芝浦工大 大宮キャンパス、大宮、埼玉  

  • 酸化ガリウム材料・デバイス研究開発の現状 Invited Domestic conference

    東脇 正高

    第157回 東工大フロンティア材料研究所学術講演会「低炭素社会に向けた次世代パワエレ最前線 ~材料からデバイスまで~」  2023.02 

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    Presentation type:Oral presentation (invited, special)  

    Venue:オンライン (Zoom)  

  • Effects of nitridation on electrical properties of Ga2O3 surface Invited International conference

    M. Higashiwaki, Z. Wang, K. Eguchi, S. Sato, S. Taniguchi, K. Nakaoka, and T. Kitada

    58th Annual Workshop on Compound Semiconductor Materials and Devices (WOCSEMMAD 2023)  2023.02 

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    Presentation type:Oral presentation (invited, special)  

    Venue:San Antonio, TX, USA  

  • 酸化ガリウムデバイス開発の現状と今後の展望 Domestic conference

    東脇 正高

    第28回 電子デバイス界面テクノロジー研究会  2023.02 

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    Presentation type:Symposium, workshop panel (nominated)  

    Venue:東レ総合研修センター、三島、静岡  

  • Beyond 5Gにおける酸化ガリウムデバイスの役割と可能性 Invited Domestic conference

    東脇 正高

    応用物理学会 薄膜・表面物理分科会 第51回薄膜・表面物理 基礎講座「Beyond 5Gと薄膜・表面物理の接点」  2022.10  応用物理学会 薄膜・表面物理分科会

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    Venue:慶應義塾大学 日吉キャンパス/オンライン (Zoom)  

  • Development of defects in (AlxGa1-x)2O3 thin films associated with Al solubility limit observed by atomic force microscopy International conference

    T. Ohtsuki and M. Higashiwaki

    4th International Workshop on Gallium Oxide and Related Materials (IWGO-4)  2022.10 

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    Presentation type:Oral presentation (general)  

    Venue:Nagano, Japan  

  • Thermodynamic analysis of group-III sesquioxide growth by molecular beam epitaxy International conference

    R. Togashi, H. Ishida, K. Goto, M. Higashiwaki, and Y. Kumagai

    4th International Workshop on Gallium Oxide and Related Materials (IWGO-4)  2022.10 

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    Presentation type:Oral presentation (general)  

    Venue:Nagano, Japan  

  • Subthreshold AC conductance of lateral Ga2O3 transistors: Mobility and carrier density in the subthreshold region International coauthorship International conference

    A. Mishra, M. J. Uren, M. Smith, M. Higashiwaki, and M. Kuball

    4th International Workshop on Gallium Oxide and Related Materials (IWGO-4)  2022.10 

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    Presentation type:Oral presentation (general)  

    Venue:Nagano, Japan  

  • Conduction processes, modeling and deep levels in nitrogen-implanted β-gallium oxide Schottky diodes International coauthorship

    C. De Santi, M. Fregolent, M. Buffolo, M. Higashiwaki, G. Meneghesso, E. Zanoni, and M. Meneghini

    4th International Workshop on Gallium Oxide and Related Materials (IWGO-4)  2022.10 

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    Presentation type:Oral presentation (general)  

    Venue:Nagano, Japan  

  • p-Si/n-Ga2O3 heterostructures fabricated by surface-activated bonding International conference

    Z. Wang, D. Takatsuki, J. Liang, T. Kitada, N. Shigekawa, and M. Higashiwaki

    4th International Workshop on Gallium Oxide and Related Materials (IWGO-4)  2022.10 

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    Presentation type:Oral presentation (general)  

    Venue:Nagano, Japan  

  • 酸化ガリウムの物性と電子デバイス応用 Invited Domestic conference

    東脇 正高

    ワイドギャップ半導体学会 特別公開シンポジウム「チュートリアル講演:ワイドギャップ半導体光・電子デバイスの最前線」  2022.10  ワイドギャップ半導体学会

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    Venue:ウインクあいち/オンライン (Zoom)  

  • 酸化ガリウムの基礎とパワーデバイスの開発動向 Invited Domestic conference

    東脇 正高

    サイエンス&テクノロジーセミナー「酸化ガリウムの基板製造・薄膜結晶成長技術およびパワーデバイスの開発動向」  2022.09  サイエンス&テクノロジー

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    Presentation type:Public lecture, seminar, tutorial, course, or other speech  

    Venue:オンライン (Zoom)  

  • セルフアラインリセスゲートGa2O3 MOSFET作製に向けたエッチングプロセスの開発 Domestic conference

    上村 崇史、東脇 正高

    第83回応用物理学会秋季学術講演会  2022.09  応用物理学会

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    Venue:東北大学 川内北キャンパス / オンライン (Zoom)  

  • Investigation of capacitance–voltage characteristics of p-Si/n-Ga2O3 heterostructures fabricated by surface-activated bonding Domestic conference

    Zhenwei Wang, Daiki Takatsuki, Jianbo Liang, Takahiro Kitada, Naoteru Shigekawa, and Masataka Higashiwaki

    The 83rd JSAP Fall Meeting  2022.09 

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    Presentation type:Oral presentation (general)  

  • Al組成の増加に伴う(AlxGa1-x)2O3薄膜の欠陥の発達 Domestic conference

    大槻 匠、東脇 正高

    第83回応用物理学会秋季学術講演会  2022.09  応用物理学会

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    Presentation type:Oral presentation (general)  

    Venue:東北大学 川内北キャンパス / オンライン (Zoom)  

  • MBE 法によるⅢ族セスキ酸化物結晶成長の熱力学的検討 Domestic conference

    富樫 理恵、石田 遥夏、後藤 健、東脇 正高、熊谷 義直

    第83回応用物理学会秋季学術講演会  2022.09  応用物理学会

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    Presentation type:Oral presentation (general)  

    Venue:東北大学 川内北キャンパス / オンライン (Zoom)  

  • Development of etching process for fabrication of Ga2O3 MOSFETs with self-aligned recessed gate

    T. Kamimura and M. Higashiwaki

    14th Topical Workshop on Heterostructure Microelectronics (TWHM 2022)  2022.08 

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    Presentation type:Oral presentation (general)  

    Venue:Hiroshima, Japan  

  • Ga2O3 device physics and engineering for power electronics and new directions Invited International conference

    M. Higashiwaki, T. Kamimura, S. Kumar, Z. Wang, T. Kitada, J. Liang, N. Shigekawa, H. Murakami, and Y. Kumagai

    15th Asia Pacific Physics Conference (APPC15)  2022.08 

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    Venue:Online (Zoom)  

  • Insights into the behavior of leakage currents and switching instability in lateral β-Ga2O3 transistors International coauthorship International conference

    Z. Chen, A. Mishra, M. Smith, M. Uren, S. Kumar, M. Higashiwaki, and M. Kuball

    5th U.S. Gallium Oxide Workshop (GOX 2022)  2022.08 

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    Presentation type:Oral presentation (general)  

    Venue:Arlington, VA, USA  

  • Ga2O3 device technologies: Power switching and high-frequency applications, and beyond Invited International conference

    M. Higashiwaki, T. Kamimura, S. Kumar, Z. Wang, T. Kitada, J. Liang, N. Shigekawa, H. Murakami, and Y. Kumagai

    5th U.S. Gallium Oxide Workshop (GOX 2022)  2022.08 

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    Presentation type:Oral presentation (keynote)  

    Venue:Arlington, VA, USA  

  • β-Ga2O3結晶の気相エピタキシャル成長の現状と展望 Invited Domestic conference

    熊谷 義直、池永 和正、石川 真人、後藤 健、村上 尚、町田 英明、倉又 朗人、山越 茂伸、東脇 正高

    化学工学会 反応工学部会 CVD反応分科会 第36回シンポジウム  2022.07  化学工学会 反応工学部会 CVD反応分科会

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    Presentation type:Oral presentation (invited, special)  

    Venue:オンライン (Zoom)  

  • Gallium oxide: Traditional but emerging semiconductor Invited International conference

    M. Higashiwaki

    International Conference on the Physics and Semiconductors 2022 (ICPS 2022)  2022.06 

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    Presentation type:Oral presentation (keynote)  

    Venue:Sydney, Australia  

  • 酸化ガリウムデバイス技術の研究開発 Invited Domestic conference

    東脇 正高

    キャンパスクリエイト「【第1回 サイエンス・サロン】~ナノテクノロジー・新材料技術における最先端研究~」  2022.06  キャンパスクリエイト

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    Venue:オンライン (Zoom)  

  • 酸化ガリウム材料・デバイスの技術動向 Invited Domestic conference

    東脇 正高

    応用物理学会 産学連携委員会 システムデバイスロードマップ産学連携委員会 (SDRJ)「2022年度 第2回BC、MtM合同委員会」  2022.06  応用物理学会 産学連携委員会 システムデバイスロードマップ産学連携委員会 (SDRJ)

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    Venue:オンライン (Zoom)  

  • Modeling of the conduction processes and deep levels in annealed nitrogen-implanted β-gallium oxide Schottky diodes International coauthorship International conference

    C. De Santi, M. Fregolent, M. Buffolo, M. Higashiwaki, G. Meneghesso, E. Zanoni, and M. Meneghini

    Compound Semiconductor Week 2022 (CSW 2022)  2022.06 

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    Presentation type:Oral presentation (general)  

  • Development of surface-activated bonding technologies to compensate for shortcomings of Ga2O3 devices Invited International conference

    M. Higashiwaki, Z. Wang, T. Kitada, N. Hatta, K. Yagi, J. Liang, and N. Shigekawa

    2022 MRS Spring Meeting and Exhibit  2022.05 

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    Presentation type:Oral presentation (invited, special)  

    Venue:Honolulu, Hawaii, USA / Online (Zoom)  

  • Ga2O3 for power electronics Invited International conference

    M. Higashiwaki

    IEEE International Symposium on Power Semiconductor Devices and ICs (ISPSD 2022)  2022.05 

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    Presentation type:Oral presentation (invited, special)  

    Venue:Vancouver, Canada / Online (Zoom)  

  • Gallium oxide power device technologies Invited International conference

    M. Higashiwaki

    2022 International Power Electronics Conference (IPEC 2022)  2022.05 

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    Presentation type:Oral presentation (invited, special)  

    Venue:Himeji, Hyogo, Japan  

  • Ga2O3イオン注入ドーピング技術とそのデバイス応用 Invited Domestic conference

    東脇 正高、Sandeep Kumar、後藤 健、村上 尚、熊谷 義直

    日本学術振興会 第R032委員会 第6回研究会「ワイドギャップ半導体Ⅱ」  2022.03  日本学術振興会 第R032委員会

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    Presentation type:Oral presentation (invited, special)  

    Venue:オンライン (Zoom)  

  • Deep levels and conduction processes in nitrogen-implanted Ga2O3 Schottky barrier diodes International coauthorship International conference

    C. De Santi, M. Fregolent, M. Buffolo, M. Higashiwaki, G. Meneghesso, E. Zanoni, and M. Meneghini

    SPIE Photonics West 2022  2022.01  SPIE

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    Presentation type:Oral presentation (general)  

    Venue:San Francisco, CA, USA  

  • Novel wide bandgap semiconductor Ga2O3 transistors Invited

    M. Higashiwaki, K. Sasaki, T. Kamimura, M. H. Wong, D. Krishnamurthy, A. Kuramata, T. Masui, S. Yamakoshi

    International Semiconductor Device Research Symposium (ISDRS 2013)  2013.12 

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    Presentation type:Oral presentation (invited, special)  

  • Structural and electrical properties of Al2O3/Ga2O3 MOS diode on β-Ga2O3 (010)

    T. Kamimura, M. H. Wong, K. Sasaki, D. Krishnamurthy, A. Kuramata, T. Masui, S. Yamakoshi, M. Higashiwaki

    2013 MRS Fall Meeting & Exhibit  2013.12 

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    Presentation type:Oral presentation (general)  

  • Depletion-mode Ga2O3 MOSFETs on β-Ga2O3 (010) substrates with Si-ion-implanted channel and contact

    M. Higashiwaki, K. Sasaki, M. H. Wong, T. Kamimura, D. Krishnamurthy, A. Kuramata, T. Masui, S. Yamakoshi

    2013 IEEE International Electron Devices Meeting (IEDM 2013)  2013.12 

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    Presentation type:Oral presentation (general)  

  • Research and development on Ga2O3 transistors and diodes Invited International conference

    M. Higashiwaki, K. Sasaki, M. H. Wong, T. Kamimura, D. Krishnamurthy, A. Kuramata, T. Masui, S. Yamakoshi

    1st IEEE Workshop on Wide Bandgap Power Devices and Applications (WiPDA 2013)  2013.10 

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    Presentation type:Oral presentation (invited, special)  

  • Research and development on Ga2O3 power devices Invited International conference

    M. Higashiwaki

    2013 International Conference on Solid State Devices and Materials (SSDM 2013)  2013.09 

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    Presentation type:Oral presentation (invited, special)  

  • Formation of low-resistance ohmic contacts on β-Ga2O3 using Si ion implantation International conference

    K. Sasaki, M. Higashiwaki, A. Kuramata, T. Masui, S. Yamakoshi

    10th Topical Workshop on Heterostructure Microelectronics (TWHM 2013)  2013.09 

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    Presentation type:Oral presentation (general)  

  • Gallium oxide (Ga2O3) transistors and diodes Invited Domestic conference

    M. Higashiwaki, K. Sasaki, T. Kamimura, M. H. Wong, D. Krishnamurthy, A. Kuramata, T. Masui, S. Yamakoshi

    2013 JSAP-MRS Joint Symposia  2013.09 

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    Presentation type:Oral presentation (invited, special)  

  • Polarized Raman spectra in β-Ga2O3 crystals Invited International conference

    T. Onuma, S. Fujioka, T. Yamaguchi, M. Higashiwaki, K. Sasaki, T. Masui, T. Honda

    17th International Conference on Crystal Growth and Epitaxy (ICCGE-17)  2013.08 

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    Presentation type:Oral presentation (general)  

  • Crystallized AlO<sub>x</sub>/AlN/GaN heterostructures grown by plasma-assisted molecular beam epitaxy

    Y. Sugiura, T. Honda, M. Higashiwaki

    10th International Conference on Nitride Semiconductors (ICNS-10)  2013.08 

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    Presentation type:Oral presentation (general)  

  • Depletion-mode Ga<sub>2</sub>O<sub>3</sub> MOSFETs

    M. Higashiwaki, K. Sasaki, T. Kamimura, M. H. Wong, D. Krishnamurthy, A. Kuramata, T. Masui, S. Yamakoshi

    71st Device Research Conference (DRC 2013)  2013.06 

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    Presentation type:Oral presentation (general)  

  • In-situ RF-MBE growth of AlO<sub>x</sub>/AlN/GaN heterostructures

    Y. Sugiura, T. Yamaguchi, T. Honda, M. Higashiwaki

    40th International Symposium on Compound Semiconductors (ISCS 2013)  2013.05 

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    Presentation type:Oral presentation (general)  

  • Growth temperature dependence of &beta;-Ga<sub>2</sub>O<sub>3</sub> homoepitaxial films by molecular beam epitaxy

    K. Sasaki, M. Higashiwaki, A. Kuramata, T. Masui, S. Yamakoshi

    40th International Symposium on Compound Semiconductors (ISCS 2013)  2013.05 

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    Presentation type:Oral presentation (general)  

  • Al<sub>2</sub>O<sub>3</sub>/n-Ga<sub>2</sub>O<sub>3</sub> metal-oxide-semiconductor diodes

    M. Higashiwaki, D. Krishnamurthy, K. Sasaki, A. Kuramata, T. Masui, S. Yamakoshi

    6th Asia-Pacific Workshop on Widegap Semiconductors (APWS 2013)  2013.05 

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    Presentation type:Oral presentation (general)  

  • Temperature dependent cathodoluminescence spectra of &beta;-Ga<sub>2</sub>O<sub>3</sub> crystals

    T. Onuma, S. Fujioka, T. Yamaguchi, M. Higashiwaki, K. Sasaki, T. Masui, T. Honda

    1st Conference on LED and Its Industrial Application (LEDIA'13)  2013.04 

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    Presentation type:Oral presentation (general)  

  • Development of gallium oxide power devices Invited

    M. Higashiwaki, K. Sasaki, A. Kuramata, T. Masui, S. Yamakoshi

    2013 DPG (German Physical Society) Spring Meeting  2013.03 

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    Presentation type:Oral presentation (invited, special)  

  • Device process techniques for gallium oxide (Ga<sub>2</sub>O<sub>3</sub>) electrical devices Invited

    M. Higashiwaki, D. Krishnamurthy, K. Sasaki, A. Kuramata, T. Masui, S. Yamakoshi

    49th Workshop on Compound Semiconductor Materials & Devices (WOCSEMMAD 2013)  2013.02 

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    Presentation type:Oral presentation (invited, special)  

  • Potential applications of wide bandgap semiconducting oxides Invited International conference

    Masataka Higashiwaki

    International Workshop on "Novel Semiconducting Oxides"  2012.10 

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    Presentation type:Symposium, workshop panel (nominated)  

  • MBE grown Ga2O3 and its power device applications Invited International conference

    K. Sasaki, M. Higashiwaki, A. Kuramata, T. Masui, S. Yamakoshi

    17th International Conference on Molecular Beam Epitaxy (MBE2012)  2012.09 

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    Presentation type:Oral presentation (invited, special)  

  • Interface Control of III-oxide/nitride composite structures Invited International conference

    M. Higashiwaki, S. Chowdhury, B. R. Swenson, U. K. Mishra, T. Igaki, T. Yamaguchi, T. Honda

    International Conference on Solid State Devices and Materials (SSDM2012)  2012.09 

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  • Single-crystal gallium oxide metal-semiconductor field-effect transistors Invited International conference

    M. Higashiwaki, K. Sasaki, A. Kuramata, T. Masui, S. Yamakoshi

    39th International Symposium on Compound Semiconductors (ISCS2012)  2012.08 

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    Presentation type:Oral presentation (invited, special)  

  • In-situ RF-MBE growth of AlOx/n-GaN composite structures International conference

    M. Higashiwaki, T. Igaki, T. Yamaguchi, T. Honda

    4th International Symposium on Growth of III-Nitrides (ISGN2012)  2012.07 

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  • New widegap semiconductor Ga2O3 MESFETs and Schottky barrier diodes Invited International conference

    M. Higashiwaki, K. Sasaki, A. Kuramata, T. Masui, S. Yamakoshi

    2012 Asia-Pacific Workshop on Fundamentals and Applications of Advanced Semiconductor Devices (AWAD2012)  2012.06 

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  • Study of Thermal Oxidation Effects on Surface Barrier Height of AlGaN/GaN Heterostructures International conference

    M. Higashiwaki, S. Chowdhury, B. L. Swenson, U. K. Mishra

    2010 International Workshop on Nitride Semiconductors (IWN2010)  2010.09 

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    Presentation type:Poster presentation  

  • Small-signal and 30-GHz power performance of AlGaN/GaN HFETs without back barriers International conference

    M. Higashiwaki, Y. Pei, R. Chu, U. K. Mishra

    67th Device Research Conference (DRC2009)  2009.06 

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  • GaN HFETs for millimeter-wave technologies Invited International conference

    M. Higashiwaki, Z. Chen, S. Keller, N. Hirose, T. Mimura, T. Matsui, U. K. Mishra

    35th International Symposium on Compound Semiconductors (ISCS)  2008.09 

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  • A comparative study of SiN deposition methods for millimeter-wave AlGaN/GaN HFETs International conference

    M. Higashiwaki, Z. Chen, Y. Pei, R. Chu, S. Keller, N. Hirose, T. Mimura, T. Matsui, U. K. Mishra

    66th Device Research Conference (DRC)  2008.06 

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  • Millimeter-wave GaN HFET technology Invited International conference

    M. Higashiwaki, T. Mimura, T. Matsui

    SPIE Photonic West  2008.01 

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  • High-frequency performance of short-gate AlGaN/GaN HFETs on SiC International conference

    M. Higashiwaki, T. Mimura, T. Matsui

    2007.09 

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  • Development of high-frequency GaN HFETs for millimeter-wave applications Invited International conference

    M. Higashiwaki, T. Mimura, T. Matsui

    7th Topical Workshop on Heterostructure Microelectronics (TWHM)  2007.08 

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  • Development of millimeter-wave GaN HFET technology Invited International conference

    M. Higashiwaki, T. Mimura, T. Matsui

    International Workshop on Nitride Semiconductors (IWN)  2006.10 

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  • GaN-based FETs using Cat-CVD SiN passivation for millimeter-wave applications Invited International conference

    M. Higashiwaki, T. Mimura, T. Matsui

    4th International Conference on Hot-Wire CVD (Cat-CVD) Process (HWCVD-4)  2006.10 

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  • AlN/GaN MIS-HFETs with Cat-CVD SiN International conference

    M. Higashiwaki, T. Mimura, T. Matsui

    33rd International Symposium on Compound Semiconductors (ISCS)  2006.08 

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  • 30-nm-gate AlGaN/GaN MIS-HFETs with 180 GHz fT International conference

    M. Higashiwaki, T. Matsui, T. Mimura

    2006.06 

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  • High-frequency AlGaN/GaN HFETs grown by plasma-assisted MBE for millimeter-wave applications Invited International conference

    M. Higashiwaki, T. Matsui, T. Mimura

    International COE Workshop on Nano Processes and Devices  2005.12 

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    Presentation type:Oral presentation (general)  

  • Influence of surface passivation using Cat-CVD SiN on electrical properties of AlGaN/GaN HFETs International conference

    M. Higashiwaki, T. Matsui, T. Mimura

    6th International Conference on Nitride Semiconductors (ICNS-6)  2005.09 

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    Presentation type:Poster presentation  

  • High fT and fmax AlGaN/GaN HFETs achieved by using thin and high-Al-composition AlGaN barrier layers and Cat-CVD SiN passivation International conference

    M. Higashiwaki, T. Matsui

    6th International Conference on Nitride Semiconductors (ICNS-6)  2005.09 

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    Presentation type:Oral presentation (general)  

  • High-frequency device performance of sub-0.1-um-gate AlGaN/GaN HFETs grown on sapphire substrates by plasma-assisted MBE International conference

    M. Higashiwaki, T. Matsui

    6th International Workshop on Heterostructure Microelectronics (TWHM)  2005.08 

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    Presentation type:Poster presentation  

  • Cat-CVD SiN insulated-gate AlGaN/GaN HFETs with 163 GHz fT and 184 GHz fmax International conference

    M. Higashiwaki, T. Matsui, T. Mimura

    63rd Device Research Conference (DRC)  2005.06 

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  • MBE growth and device characteristics of InAlN/GaN HFETs

    International Workshop on Nitride Semiconductors (IWN)  2004 

  • Plasma-assisted MBE growth of InN on low-temperature-grown InN/GaN buffer

    International Indium Nitride Workshop  2003 

  • Plasma-assisted MBE growth of InN film and InAlN/InN heterostructure

    12th International Conference on Molecular Beam Epitaxy (MBE-12)  2003 

  • Control of electron density in InN by Si doping and optical properties of Si-doped InN

    5th International Conference on Nitride Semiconductors (ICNS-5)  2003 

  • Effect of low-temperature-grown GaN intermediate layer on InN growth by plasma-assisted MBE

    International Workshop on Nitride Semiconductors (IWN)  2002 

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    Presentation type:Poster presentation  

  • Pseudomorphic In0.7Ga0.3As/In0.52Al0.48As HEMTs with super-flat interfaces fabricated on (411)A-oriented InP substrates

    International Conference on Indium Phosphide and Related Materials (IPRM)  2000 

  • GaAs/(GaAs)4(AlAs)2 quantum wire lasers grown on (775)B-oriented GaAs substrates by molecular beam epitaxy

    10th International Conference on Molecular Beam Epitaxy (MBE-10)  1998 

  • Temperature dependence of photoluminescence from high-density GaAs/(GaAs)4(AlAs)2 quantum wires grown on (775)B-oriented GaAs substrates by molecular beam epitaxy

    8th International Conference on Modulated Semiconductor Structures (MSS-8)  1997 

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    Presentation type:Poster presentation  

  • Temperature dependence of exciton lifetimes in high-density GaAs/(GaAs)4(AlAs)2 quantum wires grown on (775)B-oriented GaAs substrates by molecular beam epitaxy

    International Workshop on Nano-Physics and Electronics  1997 

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    Presentation type:Poster presentation  

  • High-density GaAs/(GaAs)2(AlAs)2 quantum wires naturally formed on (775)B-oriented GaAs substrates by molecular beam epitaxy

    9th International Conference on Molecular Beam Epitaxy (MBE-9)  1996 

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    Announcement no:WO2013-035842 

  • Ga2O3系半導体素子

    佐々木 公平 , 東脇 正高

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    property_type:Patent 

    Application no:JP2012072902 

    Announcement no:WO2013-035845 

  • Ga2O3系半導体素子

    佐々木 公平 , 東脇 正高 , 藤田 静雄

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    property_type:Patent 

    Application no:JP2012072899 

    Announcement no:WO2013-035843 

  • Ga2O3系半導体素子

    佐々木 公平 , 東脇 正高 , 藤田 静雄

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    property_type:Patent 

    Application no:JP2012072900 

    Announcement no:WO2013-035844 

  • GaN系電界効果トランジスタ

    東脇 正高

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    property_type:Patent 

    Application no:特願2006-138878 

    Announcement no:特開2007-311537 

    特開2007-311537

    J-GLOBAL

  • AlN障壁層を有するGaN系電界効果トランジスタ、及びそのような電界効果トランジスタの製造方法

    東脇 正高

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    property_type:Patent 

    Application no:特願2006-056719 

    Announcement no:特開2007-234986 

    特開2007-234986

    J-GLOBAL

  • GaN系電界効果トランジスタおよびその製造方法

    東脇 正高

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    property_type:Patent 

    Application no:JP2005016065 

    Announcement no:WO2006-022453 

    Publication no:WO2006-022453 

    J-GLOBAL

  • 窒化インジウムアルミニウム半導体の結晶成長方法

    東脇 正高

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    property_type:Patent 

    Application no:特願2004-078231 

    Announcement no:特開2005-268495 

    Patent/Registration no:特許第3876323号 

    特3876323

    J-GLOBAL

  • ヘテロ接合電界効果トランジスタ

    東脇 正高

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    property_type:Patent 

    Application no:特願2004-078228 

    Announcement no:特開2005-268493 

    特開2005-268493

    J-GLOBAL

  • 単結晶窒化インジウム膜の取得方法

    東脇 正高

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    property_type:Patent 

    Application no:特願2002-269967 

    Announcement no:特開2004-107117 

    Patent/Registration no:特許第3762992号 

    特3762992号

    J-GLOBAL

  • 窒化インジウム系化合物半導体の積層方法

    東脇 正高

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    property_type:Patent 

    Application no:特願2001-391754 

    Announcement no:特開2003-192497 

    J-GLOBAL

  • サファイア基板上への窒化インジウム積層方法

    東脇 正高

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    property_type:Patent 

    Application no:特願2001-391754 

    Announcement no:特開2003-192497 

    Patent/Registration no:特許第3671215号 

    特3671215

    J-GLOBAL

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Grant-in-Aid for Scientific Research

  • パワーデバイス応用に向けた酸化ガリウム/IV族半導体直接接合界面形成

    Grant-in-Aid for Scientific Research(B)  2019.04

  • ワイドギャップⅢ族酸化物/窒化物半導体ヘテロ構造作製のための基盤技術開拓

    Grant-in-Aid for Scientific Research(B)  2015.04

Contract research

  • 次世代省エネ型デバイス関連技術の開発・実証事業

    総務省  ICT重点技術の研究開発プロジェクト  2023.04

  • 次世代省エネ型デバイス関連技術の開発・実証事業

    2022.04

  • 次世代省エネ型デバイス関連技術の開発・実証事業

    2021.08

  • マイクロ波帯酸化ガリウムトランジスタの研究開発

    戦略的情報通信研究開発推進事業(SCOPE)  2018.04

  • 酸化ガリウムパワーデバイス基盤技術の研究開発

    内閣府  SIP(戦略的イノベーション創造プログラム)次世代パワーエレクトロニクス  2014.11

  • 超高耐圧酸化ガリウムパワーデバイスの研究

    独立行政法人新エネルギー・産業技術総合開発機構  平成23年度 省エネルギー革新技術開発事業  2011.07

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Acceptance of Researcher

  • 2023  Number of researchers:2

  • 2022  Number of researchers:1

Charge of on-campus class subject

  • 電子物理系特別演習第1(電子物性)

    2023   Intensive lecture   Graduate school

  • 電子物理工学特殊講義I

    2023   Intensive lecture   Undergraduate

  • ナノエレクトロニクス

    2023   Weekly class   Undergraduate

  • 電子物理系特別演習(電子物性)

    2023   Intensive lecture   Graduate school

  • 電子物理系特別研究(電子物性)

    2023   Intensive lecture   Graduate school

  • 電子物理工学概論2

    2023   Weekly class   Undergraduate

  • 半導体エレクトロニクス

    2023   Weekly class   Undergraduate

  • 半導体エレクトロニクス特論

    2023   Weekly class   Graduate school

  • 電子物理系特別研究第2(電子物性)

    2023   Intensive lecture   Graduate school

  • 電子物理系特別演習第2(電子物性)

    2023   Intensive lecture   Graduate school

  • 電子物理系特別演習第1(電子物性)

    2022   Intensive lecture   Graduate school

  • ナノエレクトロニクス

    2022   Weekly class   Undergraduate

  • 電子物理系特別演習(電子物性)

    2022   Intensive lecture   Graduate school

  • 半導体エレクトロニクス特論 (中百舌鳥)

    2022   Weekly class   Graduate school

  • 電子物理系特別演習第2(電子物性) (中百舌鳥)

    2022   Intensive lecture   Graduate school

  • 電子物理工学概論2

    2022   Weekly class   Undergraduate

  • 電子物理系特別研究(電子物性)

    2022   Intensive lecture   Graduate school

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Charge of off-campus class subject

  • 電子デバイス工学特論

    2011.04
    -
    2017.03
    Institution:Kogakuin University

Faculty development activities

  • 工学FDセミナー参加  2022

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    2022/09/02開催の工学FDセミナー「教育改善のためのポートフォリオシステムてぃら・みす活用法」に参加、聴講。

Number of instructed thesis, researches

  • 2023

    Number of instructed the graduation thesis:Number of graduation thesis reviews:6

    [Number of instructed the Master's Program] (previous term):[Number of instructed the Master's Program] (letter term):0

    [Number of master's thesis reviews] (chief):[Number of master's thesis reviews] (vice-chief):11

    [Number of doctoral thesis reviews] (chief):[Number of doctoral thesis reviews] (vice-chief):0

  • 2022

    Number of instructed the graduation thesis:Number of graduation thesis reviews:7

    [Number of instructed the Master's Program] (previous term):[Number of instructed the Master's Program] (letter term):0

    [Number of master's thesis reviews] (chief):[Number of master's thesis reviews] (vice-chief):15

    [Number of doctoral thesis reviews] (chief):[Number of doctoral thesis reviews] (vice-chief):0

Foreigner acceptance

  • 2023

    foreigners accepted :1

Job title

  • Job title within the department

    School of Engineering Department of Physics and Electronics 

    学科長  2024.04