Abstract
Gallium Nitride has generated significant interests for high-voltage applications due to its superior material properties such as wide bandgap, high critical electric field, high electron saturation velocity, and good thermal stability. These properties offer several potential advantages over silicon-based devices. High performance AlGaN/GaN high-electron mobility transistors (HEMTs) and Schottky Barrier Diodes (SBDs) have been realized on the silicon substrate for high-power applications in recent years, while one issue remains for these devices is the relatively high leakage current due to the quality of the buffer layer. Such a large leakage current causes serious off-state loss in the power supply and reduces the efficiency of the system. Optimization of the ohmic contacts requires not only to lowering the contact resistance to reduce power loss, but also needs to consider the buffer leakage due to ohmic metal spikes. This thesis focuses on the optimization of ohmic contacts of GaN HEMTs by using different metal stacks and rapid thermal annealing temperatures, while monitoring the buffer leakage at the same time. In addition, the impacts of using different ohmic contact alloys on HEMTs and SBDs are also analyzed. In the study of HEMTs, several layouts including one-finger, square-gate devices, and large scale devices also are used to investigate the impacts of alloyed ohmic contact on breakdown voltage such as off-state leakage. It is also observed that the turn-on voltage of the Si-diffused devices is shifted from 1.4 V to 1.27 V by diffusing silicon atoms into AlGaN/GaN layer underneath the Schottky electrode. The proposed Si-diffused ohmic contact can achieve both low contact resistance and smooth surface morphology, because the silicon atoms underneath ohmic electrode can prevent metal spikes originating from alloyed ohmic contact and improve breakdown voltage