Development and characterization of ohmic and Schottky contacts for gallium nitride and aluminum gallium nitride devices

Currently, there is strong interest in the development of III-N-based field effect transistors for microwave, high-power, and high-temperature applications. The AlGaN/GaN system is well suited for these applications due to their high electron drift velocities, high breakdown fields, and relatively good thermal conductivities. The chemical stability and mechanical hardness of the nitrides also afford these devices the latitude of operating in harsh environments. The direct energy gap of III-nitrides and their alloys also make them ideal candidates for optoelectronic devices, especially for emitters and detectors working in the green to deep-UV region of the electromagnetic spectrum. Schottky and ohmic contacts are essential building blocks for both electronic and optoelectronic devices. Due to the recent emergence of the III-N materials, contacts to these materials are poorly characterized and understood. In this work, the development and the characterization of electrical and materials performance of these contacts are presented.; Various ohmic contact schemes on p-type GaN, n-type GaN and AlGaN, as well as Schottky contacts on GaN and AlGaN were studied using a wide range of electrical and materials characterization techniques. Band gap engineering and purely process-oriented techniques such as annealing, wet and dry etching were used to improve the electrical characteristics of these contacts. Materials analyses were used to understand the evolution of electrical behavior of these contacts at higher temperatures.