T. Han and co-workers^[2] report high-performance NiO/β-Ga₂O₃ vertical heterojunction diodes (HJDs) with double-layer junction termination extension (DL-JTE) consisting of two p-typed NiO layers with varied lengths. Outstanding electronic properties including high breakdown voltage, low specific on-resistance and a power figure-of-merit (PFOM) of 5.98 GW/cm² are presented in this work, indicating that the DL-JTE structure provides a promising approach towards high-performance Ga₂O₃ HJDs.

To outline the latest advances along with the opportunities and challenges of Ga₂O₃ technologies, we organized a Special Issue on “Towards high performance Ga₂O₃ electronics”, which will be published in two consecutive issues on Journal of Semiconductors. The first 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. This issue looks at the focus topic on power devices and DUV optoelectronic devices for Ga₂O₃ semiconductors and the application in advanced high-power electronic devices, consisting of eight research articles, one timely review and one Comments & Opinions.

Currently β-Ga₂O₃ is therefore mainly used in unipolar devices because of the challenge to obtain stable p-type β-Ga₂O₃, including Schottky barrier diodes (SBDs) and field-effect transistors (FETs).

Nevertheless, the absence of p-type Ga₂O₃ is a main difficulty for the bipolar devices. To conquer this challenge, a natively p-typed oxide of NiO is proved to be greatly suitable for β-Ga₂O₃ power devices.

Ga₂O₃, as an ultra-wide bandgap semiconductor with their bandgap directly corresponding to the DUV region, provides a new scheme to deliver massively enhanced device performance for filter-free DUV photodetectors. Furthermore, the persistent photoconductivity (PPC) effect exhibited by its amorphous counterpart suggests new applications in neuromorphic computing.

Z. Jiang and co-workers^[3] experimentally show the instability mechanisms for a NiO/β-Ga₂O₃ heterojunction-gate field effect transistor (HJ-FET) under different gate stress voltage (V_G,s) and stress times (t_s), it is identified that there are two different degradation mechanisms of the devices under negative bias stress (NBS), offering an important theoretical guide to study the reliability of NiO/β-Ga₂O₃ heterojunction devices in power electronic applications.

We are excited to share these timely reviews and advanced research results on the field of Ga₂O₃ electronics with the readership of Journal of Semiconductors. We sincerely hope that this Special Issue will provide the readers with a meaningful and profound overview of the recent progress, opportunities and challenges of power devices and DUV optoelectronic devices for Ga₂O₃ semiconductors. 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.

To fully utilize the application potential of β-Ga₂O₃, the large-area structures are needed to sustain a high on-state current for practical applications and yet demanding in the quest for the thermal effect and circuit applications.

J. Tao and co-workers^[6] demonstrate a high-performance ultraviolet-visible (UV-VIS) photodetector based on a TiO₂@GaO_xN_y-Ag ternary heterostructure. Excellent optoelectronic characteristics, including superb responsivity and detectivity particular, could be mainly attributed to the synergistic effect of the type-Ⅱ band structure of the metal–semiconductor–metal heterojunction and the plasmon resonance effect of Ag.

Gallium oxide (Ga₂O₃) has garnered world-wide attention as an ultrawide-bandgap semiconductor material from the area of power electronics and DUV optical devices benefiting from its outstanding electronic and optoelectronic properties. For one thing, since Ga₂O₃ features high critical breakdown field of 8 MV/cm and Baliga’s figure of merit (BFOM) of 3444, it is a promising candidate for advanced high-power applications. For another thing, due to the bandgap directly corresponding to the deep-ultraviolet (DUV) region, Ga₂O₃ is widely used in DUV optoelectronic devices.

W. Guo and co-workers^[5] present superb large-area vertical β-Ga₂O₃ SBDs with a Schottky contact area of 1 × 1 mm² and achieve a high-efficiency DC–DC converter based on the device. Superior electronic properties including outstanding forward characteristics, low on-resistance (R_on), high breakdown voltage and a conversion efficiency of 95.81% are presented in this work, indicating the great potential of Ga₂O₃ SBDs and relevant circuits in power electronic applications.

β-Ga₂O₃ SBDs have been intensively studied and undergone rapid progress since the early 2010s and have achieved remarkable results. Interpreting and understanding the temperature dependent β-Ga₂O₃ SBDs characteristics and the dominate conduction mechanisms are critical for improving SBD performance.

In the Comments & Opinions, G. Xu and co-workers^[10] provide an insightful discussion on the development of vertical β-Ga₂O₃ power electronics covering various surface/interface engineering, diverse edge termination and quasi-inversion vertical transistor. The existing problems of gallium oxide power devices including high defect density and severe interface damage of large area devices, lack of p-type doping and low thermal conductivity are further shown in this article. Building the current blocking layers (CBLs) formed by oxygen annealing/N-implantation/in situ epitaxy can minimize punch-through current and improve breakdown voltage of β-Ga₂O₃ transistors, the authors highlight the U-MOSFET may be the way out for β-Ga₂O₃ power transistors.

Ga₂O₃ based flexible heterojunction type DUV photodetectors show excellent solar blind photoelectric performance which makes them ideal for use in intelligent wearable devices. C. Wu and co-workers^[7] present a novel self-healing and self-powered photodetector based on PEDOT: PSS/Ga₂O₃ active layer and a hydrogel substrate. Remarkable recovery capability and the photodetector’s superior photoelectric performance were achieved showing new possibilities to develop wearable and intelligent electronics in the future.

Optoelectronic synapse and neuromorphic computing propose a new structure that differs from conventional von Neumann architecture, offering the benefits of low power consumption, high transmission rate, wide bandwidth and security. R. Li and co-workers^[8] demonstrate an homojunction-based multi-functional optoelectronic synapse (MOLS) with an Al/Ga₂O₃(oxygen-deficient)/Ga₂O₃(oxygen-rich)/ITO vertical structure and modulated with dual-band wavelength illumination to mimic biological synaptic behaviors such as PPF and SNDP. The MOLS exhibited the performances of associative learning and logic gates, paving the way for in-sensor and parallel computation in neural morphology devices.

M. Labed and co-workers^[1] analyze the W/β-Ga₂O₃ Schottky barrier diodes deposited by confined magnetic field-based sputtering (CMFS) at different operation temperatures. Temperature dependent SBD parameters including the Schottky barrier height, ideality factor, the series and on-resistances are shown in this work. The interfacial dislocation extracted from the tunneling current was further presented, suggesting the domination of tunneling through dislocation in the transport mechanism.

Y. Zhang and co-worker^[9] summarize and discuss the anisotropic properties and applications of β-Ga₂O₃, anisotropic optical properties including optical bandgap, Raman and photoluminescence characters are comprehensively reviewed. In addition, the anisotropy in electron mobility and affinity are discussed. Finally, the applications, especially polarization photodetectors, based on β-Ga₂O₃ were summarized comprehensively.

X. Zhou and co-workers^[4] demonstrate a multi-finger MOSFET with output current reach to 0.5 A. To critically investigate the self-heating effect, the authors highlight the generation and dissipation actions by analyzing the electrical characteristics, heat dissipation of the device and the relationship between device temperature and time/bias.