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By
James S. Speck;
James S. Speck
Materials Department,
University of California
, Santa Barbara, Santa Barbara, California 93106,
USA
Search for other works by this author on:
Esmat Farzana
Esmat Farzana
Materials Department,
University of California
, Santa Barbara, Santa Barbara, California 93106,
USA
Search for other works by this author on:

Beta-phase gallium oxide (β-Ga2O3) is a material of growing interest as a potential next-generation power semiconductor with its ultrawide bandgap, predicted breakdown field, and affordability of native substrates. Ultrawide Bandgap β-Ga2O3 Semiconductor: Theory and Applications is a comprehensive overview of β-Ga2O3 semiconductor and its application in power electronic devices. It introduces readers to fundamental properties, addresses recent developments and existing challenges in growth and devices of β-Ga2O3, and offers insights to the future direction of commercialization through chip and circuit integration.

Covering a wide range of power devices, the book discusses:

  • The properties of β-Ga2O3 that make it a potential next-generation semiconductor material

  • A variety of techniques for producing and modifying β-Ga2O3 electronic properties

  • An introduction to device concepts, fabrication, and functionality evaluation for prospective high power, high-frequency, and extreme-environment applications

  • Commercialization challenges and how they may be addressed to make them a viable option

Ultrawide Bandgap β-Ga2O3 Semiconductor: Theory and Applications answers the needs of both researchers and professionals in semiconductor devices, electronic materials, solid-state physics, consumer electronics, communications, and all other industries reliant on semiconductors.

James S. Speck, Ph.D., is a Distinguished Professor and Seoul Viosys Chair in the Materials Department at the University of California, Santa Barbara (UCSB), and an elected Fellow of the National Academy of Inventors. He received his B.S.M.E. degree in Metallurgical Engineering from the University of Michigan in 1983 and S.M. and Sc.D. in Materials Science from the Massachusetts Institute of Technology in 1985 and 1989, respectively. For over 25 years, his group has pioneered the research in wide bandgap nitride semiconductors including epitaxial growth, heterostructures, transport, and defect minimization to improve the efficiency of optoelectronic devices, such as UV and visible light emitting diodes and high-voltage power diodes. His group has also formed the foundation of growth and materials science of epitaxial oxides and ferroelectric oxide films and is currently actively investigating the emerging ultrawide-bandgap oxide semiconductor, β-Ga2O3. Professor Speck is the recipient of numerous prestigious awards, including the International Symposium on Compound Semiconductors Quantum Device Award, the University of Michigan Alumni Society Merit Award, and the IEEE Photonics Society Aron Kressel Award. He was also named an inaugural Materials Research Society Fellow and American Physical Society Fellow in 2008 and 2009, respectively.

Esmat Farzana, Ph.D., is currently a Postdoctoral Researcher in the Materials Department at the University of California, Santa Barbara (UCSB), working with Professor James S. Speck and Professor Sriram Krishnamoorthy. She received her Ph.D. in Electrical and Computer Engineering from The Ohio State University (OSU) in 2019 under Professor Steven A. Ringel and B.S. in Electrical Engineering from Bangladesh University of Engineering and Technology in 2011. Her Ph.D. research in advanced electronic characterization of β-Ga2O3 has led to a comprehensive understanding of its defects within the ultrawide bandgap to refine its growth and doping properties. Her current research at UCSB involves device design and fabrication with β-Ga2O3 and III-nitrides that integrate challenges for high-voltage and extreme radiation applications. Her lead-author publications have been featured as Editor's Picks in APL Materials, IEEE Electron Device Letters, and Applied Physics Letters. She was selected to be a Rising Star in EECS in 2020.

Fikadu Alema

Agnitron Technology Inc., 8360 Commerce Dr, Chanhassen, Minnesota 55317

Aaron R. Arehart

Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210

Andrea Arias-Purdue

Teledyne Scientific Company, Thousand Oaks, California 91360, USA

Arkka Bhattacharyya

Materials Department, University of California, Santa Barbara, Santa Barbara, California 93106, USA

J. D. Blevins

Principal Materials Engineer, Air Force Research Laboratory Materials and Manufacturing Directorate, AFRL/RXME, 2977 Hobson Way, Wright-Patterson AFB, Ohio 45433, USA

Kelson D. Chabak

Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433, USA

Esmat Farzana

Materials Department, University of California, Santa Barbara, Santa Barbara, California 93106, USA

Hemant J. Ghadi

Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210

Krishnendu Ghosh

Department of Electrical Engineering, University at Buffalo, Buffalo, New York 14260, USA

Andrew J. Green

Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433, USA

Oliver Hilt

Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Straße 4, 12489 Berlin, Germany

Hsien-Chih Huang

Department of Electrical and Computer Engineering, Holonyak Micro and Nanotechnology Laboratory, University of Illinois, Urbana, Illinois 61801

Jinwoo Hwang

Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210, USA

Sriram Krishnamoorthy

Materials Department, University of California, Santa Barbara, Santa Barbara, California 93106, USA

Avinash Kumar

Department of Electrical Engineering, University at Buffalo, Buffalo, New York 14260, USA

Xiuling Li

Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas 78712

Kyle J. Liddy

Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433, USA

Akhil Mauze

Materials Department, University of California, Santa Barbara, Santa Barbara, California 93106, USA

Joe F. McGlone

Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210

Vivek Mehrotra

Teledyne Scientific Company, Thousand Oaks, California 91360, USA

Sai Mu

Materials Department, University of California, Santa Barbara, Santa Barbara, California 93106, USADepartment of Physics and Astronomy, University of South Carolina, Columbia, South Carolina 29208, USA

Charles Neft

Teledyne Scientific Company, Thousand Oaks, California 91360, USA

Andrei Osinsky

Agnitron Technology Inc., 8360 Commerce Dr, Chanhassen, Minnesota 55317

Praneeth Ranga

Department of Electrical and Computer Engineering, The University of Utah, Salt Lake City, Utah 84112, USA

Steven A. Ringel

Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210

George Seryogin

Agnitron Technology Inc., 8360 Commerce Dr, Chanhassen, Minnesota 55317

Keisuke Shinohara

Teledyne Scientific Company, Thousand Oaks, California 91360, USA

Uttam Singisetti

Department of Electrical Engineering, University at Buffalo, Buffalo, New York 14260, USA

James S. Speck

Materials Department, University of California, Santa Barbara, Santa Barbara, California 93106, USA

Kornelius Tetzner

Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Straße 4, 12489 Berlin, Germany

Darren Thomson

Senior Materials Research Engineer, Air Force Research Laboratory, Sensors Directorate, 2241 Avionics Circle, Bldg. 600, Wright-Patterson AFB, Ohio 45433

Miguel E. Urteaga

Teledyne Scientific Company, Thousand Oaks, California 91360, USA

Joel B. Varley

Materials Science Division, Lawrence Livermore National Laboratory, Livermore, California 94551, USA

Chris G. Van de Walle

Materials Department, University of California, Santa Barbara, Santa Barbara, California 93106, USA

Mengen Wang

Materials Department, University of California, Santa Barbara, Santa Barbara, California 93106, USA

Man Hoi Wong

Department of Electronic and Computer Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong

Joachim Würfl

Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Straße 4, 12489 Berlin, Germany

Power electronics, using wide-bandgap semiconductors, has been a fast growing field in recent years driven by the need of energy-efficient power systems, low carbon economy, and reaching the ever wider voltage range of emerging commercial and consumer application areas. This book has been developed focusing on these new generation of power semiconductors, particularly β-Ga2O3, for a topical graduate course in electrical engineering and materials science. For graduate students interested in power electronics, it is important to develop their knowledge integrating both materials and devices to connect the power semiconductor properties with device physics, design, and the ultimate performance in high-voltage applications. Although it is challenging to merge these different aspects within a limited scope of a book, we aimed through this book to enable the reader with a thorough grasp of basic concepts as well as an overview of advanced knowledge by incorporating the latest progress in the field. Thus, this book can also be a useful reference material for academic and industrial research specialists, including postdocs, faculties, national lab scientist, and industrial scientists, who are diligently working in the area of β-Ga2O3 and other wide-bandgap semiconductors in power electronics.

This book has been organized with selected topics for the chapters, with multiple chapters covering different areas of the field of β-Ga2O3 materials and state-of-the-art devices. The introductory chapter first starts out with fundamental power switch concepts and the advantageous prospects of wide bandgap semiconductors in power devices, in conjunction with the ultrawide-bandgap β-Ga2O3 properties, material growth, devices, and high-voltage application challenges. These will also foreshadow the contents of the remaining chapters of the book that discuss these topics separately in detail.

A major excitement for β-Ga2O3 is its available melt-grown native substrates that will ideally realize an ultrawide-bandgap power electronics technology free from device-degrading dislocations. These dislocations, in fact, are critical challenges in the concurrent wide-bandgap GaN and AlGaN devices to reach their predicted performance and reliability that must be managed, even after two decades of development. To recognize this key advantage of β-Ga2O3, we included a subsequent chapter on bulk crystal growth of β-Ga2O3 from different melt-based techniques that have been adapted for large-scale manufacturing of β-Ga2O3 substrates in USA (Synoptics) and Japan (Novel Crystal Technology). We have then provided a background of some prominent epitaxy growth methods of β-Ga2O3 necessary to realize the high-quality power devices, such as molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD).

The power device transport and breakdown performance are largely dependent on the electronic properties of each device component, such as drift layer, channel, contact layers, buffer, and current-blocking layer. As such, we included the control of electronic properties of β-Ga2O3 through doping capability and compensation effects in the relevant growth chapters of bulk crystal, MBE, and MOCVD. Subsequently, we organized the specifically focused doping and defect related chapters combining density functional theory with experimental microscopy and spectroscopy studies (thermal, optical, or frequency-based methods) so that readers can coherently correlate the origin and role of impurities in β-Ga2O3 complementing theory with experiments.

This book has also been developed as a comprehensive resource of β-Ga2O3 state-of-the-art devices that will be of value to the power device researchers. The high-voltage β-Ga2O3 device development requires an understanding of physical phenomena under an applied field. For this purpose, we discussed the electric field effects on mobility, impurity scattering, phonon interaction, and impact ionization in β-Ga2O3 to conceptualize the transport and breakdown phenomena. The latter part of this book covers a wide range of β-Ga2O3 power devices with their design principle in both vertical and lateral topologies. Vertical power rectifiers are first discussed with high-field management techniques that can prevent premature breakdown in high-voltage operation, such as field plates, guard rings, trench diodes, ion implantation, mesa termination, and extreme permittivity dielectrics. Afterward, we moved to advanced lateral power transistors, including the design strategy of different gate and field plate architectures with their performance characteristics. Scaled lateral transistors with delta-doping and modulation doping are also included as a means to obtain high mobility channels for high-power and high-frequency devices. Specific importance has been given in device fabrication by including process details in each relevant chapter as well as with a focused chapter on low-damage wet etch and metal-assisted chemical etching of β-Ga2O3.

Finally, the challenges of β-Ga2O3 devices in the prospective extreme environments, such as high-temperature and harsh radiation, have been addressed with thermal management and radiation effects to demonstrate the performance and reliability concerns during device application lifetime. The last chapter has delved into the prospects of β-Ga2O3 in chip and circuit integration with discussions on high-frequency switching loss, conduction loss, and β-Ga2O3-based buck and boost converters. This chapter, contributed by the experts in power circuits at Teledyne Scientific and Air Force Research Laboratory, will certainly act as a guideline to make β-Ga2O3 competitive at the power circuit level with the existing more mature technology of GaN and SiC.

James S. Speck and Esmat Farzana

Materials Department, University of California, Santa Barbara

The editors express their gratitude to Dr. Ali Sayir for providing the funding support through the Multi-disciplinary University Research Initiative (MURI) initiated by the Air Force Office of Scientific Research (AFOSR) that fostered the understanding of β-Ga2O3 materials and device development, with fruitful collaborative efforts from multiple universities including University of California, Santa Barbara, The Ohio State University, Georgia Institute of Technology, University of Massachusetts Lowell, University at Buffalo, The University of Utah, and the research industry, Agnitron Technology.

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