| There is a strong interest in the development of AlGaN/GaN enhancement- and depletion-mode high-electron-mobility transistors (HEMTS) for application in high power, high frequency, and harsh environment applications. The GaN-based materials have excellent properties for these types of applications, including wide, direct bandgaps between 3.4 eV for GaN and 6.2 eV for AlGaN, high electron mobility (1000 cm2/V·s in GaN; higher in AlGaN/GaN heterostructures), high thermal conductivity (1.5 W/cm·K), and high breakdown strength (5 MV/cm). Extensive progress has been made in the last decade towards development of GaN-based depletion-mode HEMTS (D-HEMTS), which are beginning to atttract commercial interest for high-power solid-state microwave amplifiers, particularly for telecommunications applications. Integrating D-HEMTS with enhancement-mode HEMTS (E-HEMTS) allows increased circuit complexity with smaller die size and lower power consumption, but research into GaN-based E-HEMTS has lagged behind that into D-HEMTS due to difficulties inherent in growth and processing of the GaN-based materials.; This dissertation documents the development of high-performance gate-recessed HEMTs in the AlGaN-GaN material system. The primary goal of the dissertation research is the development of processes that are suitable for fabrication of AlGaN/GaN HEMTs with precise threshold voltage control for both enhancement- and depletion-mode operation. The specific areas of research include controllable and low-damage gate-recess etching, damage-removing annealing processes, and metal structures for Schottky gate contacts. Both E-HEMTs and D-HEMTs are made in order to study the effect of recess etching, post-etch annealing, and post gate annealing processes on device characteristics. |
