AlGaN/GaN high electron mobility transistors (HEMTs) are regarded as promising candidates for a 5G communication system, which demands higher frequency and power. Source/drain ohmic contact is one of the key fabrication processes crucial to the device performance. Firstly, Au-contained metal stacks combined with RTA high-temperature ohmic contact schemes were presented and analyzed, including process conditions and contact formation mechanisms. Considering the issues with the Au-contained technique, the overview of a sequence of Au-free schemes is given and comprehensively discussed. In addition, in order to solve various problems caused by high-temperature conditions, novel annealing techniques including microwave annealing (MWA) and laser annealing (LA) were proposed to form Au-free low-temperature ohmic contact to AlGaN/GaN HEMT. The effects of the annealing method on surface morphology, gate leakage, dynamic on-resistance (R_ON), and other device characteristics are investigated and presented in this paper. By using a low-temperature annealing atmosphere or selective annealing method, gate-first Si-CMOS compatible AlGaN/GaN HEMT technology can be realized for high frequency and power application.

β-Ga₂O₃, with excellent bandgap, breakdown field, and thermal stability properties, is considered to be one of the most promising candidates for power devices including field-effect transistors (FETs) and for other applications such as Schottky barrier diodes (SBDs) and solar-blind ultraviolet photodetectors. Ohmic contact is one of the key steps in the β-Ga₂O₃ device fabrication process for power applications. Ohmic contact techniques have been developed in recent years, and they are summarized in this review. First, the basic theory of metal–semiconductor contact is introduced. After that, the representative literature related to Ohmic contact with β-Ga₂O₃ is summarized and analyzed, including the electrical properties, interface microstructure, Ohmic contact formation mechanism, and contact reliability. In addition, the promising alternative schemes, including novel annealing techniques and Au-free contact materials, which are compatible with the CMOS process, are discussed. This review will help our theoretical understanding of Ohmic contact in β-Ga₂O₃ devices as well as the development trends of Ohmic contact schemes.

This review introduced selected experimental and numerical studies of β-Ga₂O₃ power field-effect transistors, with emphasis on lateral and vertical metal–oxide–semiconductor field-effect transistors (MOSFETs), heterojunction devices, and superjunction-related concepts. Device classes are distinguished by a gate control, current-flow direction, and charge-compensation mechanism. Diode and capacitor studies are also included because they form transistor contacts and gate stacks. Four benchmark tables organize 30 device configurations, separating fabricated devices from numerical concepts and retaining source-specific resistance normalization, operating conditions, and evidence limitations. The synthesis links reported performance gains to their conduction, interface, and thermal costs. Intrinsic material estimates, measured device capabilities, and projected circuit benefits are assessed separately. Incomplete normalization and parameter pairing constrain cross-study comparisons, while dynamic resistance, gate-stack lifetime, electrothermal failure, and reproducibility remain architecture-dependent validation needs. Static breakdown voltage alone does not establish switching performance, manufacturing yield, or commercialization readiness. This review will help our theoretical understanding of β-Ga₂O₃ power MOSFETs as well as the development trends of β-Ga₂O₃ power application schemes.