Current Status of Research on High‐Electron‐Mobility Transistor Devices on Gallium Nitride and Aluminum Nitride Substrates

ABSTRACT Gallium nitride‐based high‐electron‐mobility transistors (GaN HEMTs) are widely used in fields such as microwave communications and power electronics due to their excellent properties, including a wide bandgap, high critical breakdown field strength, and high electron mobility. Although commercial GaN HEMTs on foreign substrates (Si, SiC, and sapphire) are widely adopted, unavoidable heteroepitaxial mismatches in lattice and thermal expansion introduce high dislocation densities, exacerbating current collapse and leakage. This paper systematically reviews the material properties and structural advantages of free‐standing GaN and AlN single‐crystal substrates, detailing the latest research progress on GaN‐substrate HEMTs in terms of substrate doping engineering, buffer layer optimization, and enhancement‐mode device design. The key technological breakthroughs of AlN‐substrate HEMTs in GaN and high‐Al‐content AlGaN channel devices were also explored. It compares the application potential and core challenges of these two technical routes, outlines future development directions, and provides a systematic reference for the research and development of GaN‐based power and RF devices.