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 onJournal 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-dopedβ-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 epitaxialβ-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-dopeβ-Ga₂O₃ films. W. Wang and co-workers^[2] discuss the epitaxial relationship and electronic behaviour ofα-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 forα-Ga₂O₃ thin films with different crystal orientations. Oxygen vacancy level variation of differently-orientedα-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-qualityα-Ga₂O₃ films. Large-scale and uniformα-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 ofβ-Ga₂O₃ thin films on sapphire substrates using the carbothermal reduction method. Optimized growth parameters were experimentally investigated and obtained for the high-qualityβ-Ga₂O₃ epitaxial thin films. The authors’ results indicate that the carbothermal reduction method could be a viable technique forβ-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-dopedβ-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-modeβ-Ga₂O₃ enabled field-effect transistors (E-mode FETs), covering the material growth, device fabrication and typical device properties. It is concluded thatβ-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 ofβ-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 ofJournal 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 ofJournal of Semiconductors for their warm help.

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.