Design, fabrication, and characterization of normally-off GaN HEMTS

GaN-based high-electron-mobility transistors (HEMTs) have been developing rapidly from the time when they were first demonstrated in the 1990s. They have consistently been presented as a displacement technology to silicon based power devices owing to the superior material properties of GaN such as high-electric breakdown field, high-electron saturation velocity, and high mobility. Normally-off GaN HEMT devices are particularly significant in power electronics applications. In this thesis, a comprehensive study of normally-off high-electron-mobility transistors is presented, including theoretical background review, theoretical analysis, physically-based device simulations, device fabrication and optimization and electrical characterization. p-GaN gate InAlN/GaN HEMT and recessed AlGaN/GaN MISHEMT devices have been successfully demonstrated.