There is currently great optimism within the electronics community that gallium oxide (Ga2O3) ultra-wide bandgap semiconductors have unprecedented prospects for eventually revolutionizing a rich variety of power electronic applications. Specially, benefiting from its ultra-high bandgap of around 4.8 eV, it is expected that the emerging Ga2O3 technology would offer an exciting platform to deliver massively enhanced device performance for power electronics and even completely new applications. High-quality Ga2O3 thin films are critical and yet demanding in the quest for power electronic devices with desired performance. Therefore, with the advent of Ga2O3-enabled power device systems, effective epitaxy techniques that can achieve the scalable synthesis of high-quality Ga2O3 thin films are urgently required.
To outline the latest advances along with the opportunities and challenges of Ga2O3 technologies, we organised a Special Issue on “Towards high performance Ga2O3 electronics”, which will be published in two consecutive issues on Journal of Semiconductors. This issue features a collection of cutting-edge advances focused on thin film epitaxy techniques for Ga2O3 semiconductors and their application in innovative power electronic devices, consisting of six research articles, two timely reviews and one Comments & Opinions. W. Tang and co-workers[1] report the homoepitaxial growth of Si-doped β-Ga2O3 thin films on semi-insulating (100) β-Ga2O3 single crystal substrates through metalorganic chemical vapor deposition (MOCVD) method. With careful optimization of growth conditions, high-quality epitaxial β-Ga2O3 layers with adjustable Si-doping concentration were realized using the MOCVD epitaxy approach. Outstanding electronic properties including high electron mobility and low contact resistance are further shown in this work, suggesting high-performance electronic devices based on the Si-dope β-Ga2O3 films. W. Wang and co-workers[2] discuss the epitaxial relationship and electronic behaviour of α-Ga2O3 thin films depending on the crystal orientation of the sapphire substrates. Physical properties including crystalline structure, optical bandgap and electrical conductivity were thoroughly investigated for α-Ga2O3 thin films with different crystal orientations. Oxygen vacancy level variation of differently-oriented α-Ga2O3 thin films has been proposed as the origin for the observed difference in physical properties. X. Wang and co-workers[3] experimentally show a mist-CVD-based rapid epitaxy technique for the fabrication of high-quality α-Ga2O3 films. Large-scale and uniform α-Ga2O3 thin films up to 2-inch were demonstrated to be grown on sapphire substrates. Related thin film growth mechanisms were investigated by performing comprehensive crystal structure characterizations. L. Cheng and co-workers[4] present the study of the hetero-epitaxy of β-Ga2O3 thin films on sapphire substrates using the carbothermal reduction method. Optimized growth parameters were experimentally investigated and obtained for the high-quality β-Ga2O3 epitaxial thin films. The authors’ results indicate that the carbothermal reduction method could be a viable technique for β-Ga2O3 thin film deposition. Beyond the application of Ga2O3 on electronic devices, L. Li and co-workers[5] report their recent progress on Sn-doped Ga2O3 thin film enabled high-performance solar-blind photodetectors. The effect of different post-annealing gas conditions was investigated for radio frequency magnetron sputtering prepared Sn-doped β-Ga2O3 films. Y. Wang and co-workers[6] developed a CVD method for centimetre-scale Ga2O3 microwire growth and demonstrated photodetectors based on the fabricated Ga2O3 microwires. They show that microwires of single crystalline Ga2O3 can be obtained reaching up to 1 cm in length. Leveraging the high crystal quality, Ga2O3 microwire-based metal-semiconductor-metal photodetectors were achieved showing excellent solar-blind photodetection behaviour. B. Li and co-workers[7] present a timely account of recent advances in enhancement-mode β-Ga2O3 enabled field-effect transistors (E-mode FETs), covering the material growth, device fabrication and typical device properties. It is concluded that β-Ga2O3-based E-mode FETs, as a promising device concept, could drive exciting innovations for power electronics. The authors also discussed the key challenges and future development of β-Ga2O3-based E-mode FETs. Nickel oxide (NiO) has been identified as a promising wide-bandgap p-type semiconductor complementary to the n-type Ga2O3. X. Lu and co-workers[8] summarize and discuss recent advances and challenges of NiO/Ga2O3 heterojunction enabled power electronic devices. Recent progress regarding the construction and characterization methods as well as the device technology for NiO/Ga2O3 heterojunctions are critically surveyed. Furthermore, future challenges and opportunities of NiO/Ga2O3 heterojunction-based power electronic devices are discussed. In the Comments & Opinions, G. Han and co-workers[9] provide an insightful discussion on the status quo and future opportunities of the heterogeneous integration technologies for Ga2O3 thin film-based power devices. Building Ga2O3 power devices urgently requires an efficient thermal management strategy due to the intrinsically low thermal conductivity of the Ga2O3 itself, which thus inspires new ways to realize “cool” devices. By critically surveying the existing technologies that can address the thermal management challenge of Ga2O3 power devices, the authors highlight the ion-cutting based heterogeneous integration as a promising approach towards scalable production of high-performance power devices with high thermal stability.
We are delighted to share these timely reviews and exciting research results on the field of Ga2O3 electronics with the readership of Journal of Semiconductors. We hope that this Special Issue will provide the readers with an overview of the recent progress, opportunities and challenges of Ga2O3 thin film epitaxy technology and power devices. We would like to thank all the authors for their great contributions to this Special Issue. We are also grateful to the editorial and production staff of Journal of Semiconductors for their warm help.
Genquan Han：is a full professor at Xidian University and a recipient of the National Science Fund for Distinguished Young Scholars. He graduated from Tsinghua University with a bachelor's degree and received his Ph.D. from the Institute of Semiconductors, Chinese Academy of Sciences in 2008. After graduation, he joined the National University of Singapore to conduct research on advanced microelectronic devices and made original contributions in the field of advanced CMOS device research. Since returning to China in 2013, he has mainly focused on research in wide-bandgap gallium oxide (Ga2O3) heterojunction integrated materials and power devices, post-Moore new micro/nano devices and chips. He serves as an editor for IEEE Electron Device Letters
Shibing Long：is a full professor at the Institute of Microelectronics, University of Science and Technology of China. He received his Ph.D. from the Institute of Microelectronics of the Chinese Academy of Sciences in 2005. Then, he worked there from 2005 to 2018 and joined the University of Science and Technology of China in 2018. His research focuses on micro- and nano-fabrication, RRAM, ultrawide bandgap semiconductor devices (power devices and detectors) and memory circuit design
Yuhao Zhang：received the B.S. degree from Peking University, Beijing, China, in 2011, and the M.S. and Ph.D. degrees from Massachusetts Institute of Technology (MIT), Cambridge, MA, USA, in 2013 and 2017, respectively. From 2017 to 2018, he was a postdoctoral associate with MIT. Since 2018, he has been an Assistant Professor with the Center for Power Electronics Systems, the Bradley Department of Electrical and Computer Engineering, Virginia Tech. His research interests include power semiconductor devices, (ultra-)wide-bandgap semiconductor materials, power electronics applications, and machine learning assisted co-design
Yibo Wang：received his B.S. from Chongqing University (China) in 2014, and Ph.D. from Xidian University (China) in 2021. From 2022, he worked as an Assistant Research Fellow in Prof. Ke Xu’s Group at Suzhou Institute of Nano-Tech and Nano-Bionics (SINANO), Chinese Academy of Sciences. His research interests include Ga2O3 power devices and vertical GaN devices, and has done some works about the heterogeneous integration and superjunction Ga2O3 power transistors
Zhongming Wei：received his B.S. from Wuhan University (China) in 2005, and Ph.D. from Institute of Chemistry, Chinese Academy of Sciences in 2010 under the supervision of Prof. Daoben Zhu and Prof. Wei Xu. From August 2010 to January 2015, he worked as a postdoctoral fellow and then Assistant Professor in Prof. Thomas Bjørnholm's group at University of Copenhagen, Denmark. Currently, he is working as a Professor at Institute of Semiconductors, Chinese Academy of Sciences. His research interests include low-dimensional semiconductors and their optoelectronic devices
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