Group III-nitride devices and applications

Abstract

The group III-nitride system of materials has had considerable commercial success in recent years in the solid state lighting (SSL) and power electronics markets. The need for high efficient general lighting applications has driven research into InGaN based blue light emitting diodes (LEDs), and demand for more efficient power electronics for telecommunications has driven research into AlGaN based high electron mobility transistors (HEMTs). However, the group III-nitrides material properties make them attractive for several other applications that have not received as much attention. This work focuses on developing group III-nitride based devices for novel applications. GaN is a robust, chemically inert, piezoelectric material, making it an ideal candidate for surface acoustic wave (SAW) devices designed for high temperature and/or harsh environment sensors. In this work, SAW devices based on GaN are developed for use in high temperature gas or chemical sensor applications. To increase device sensitivity, while maintaining a simple one-step photolithography fabrication process, devices were designed to operate at high harmonic frequencies. This allows for GHz regime operation without sub-micron fabrication. One potential market for this technology is continuous emissions monitoring of combustion gas vehicles. In addition to SAW devices, high electron mobility transistors (HEMTs) were developed. The epitaxial structure was characterized and the 2-D electron gas concentrations were simulated and compared to experimental results. Device fabrication processes were developed and are outlined. Fabricated devices were electrically measured and device performance is discussed. Above all, I would like to thank my wife, Jackie, whose patience, loving support, and commitment to our family allowed me to pursue this degree. She deserves as much, if not more credit for her willingness to leave all her family and friends behind in San Diego, move to Morgantown, WV with me, and raise our son while I attended school. I would like to thank my son, Joshua, who even at a young age, showed interest and enthusiasm in my work. His questions helped me think about this work in ways I would not have otherwise. I would like to thank my advisor, Dr. Dimitris Korakakis, for taking the chance, and giving me the opportunity to conduct this research. His time, discussions, guidance and mentoring were invaluable. Not only for progressing this work, but for helping me establish a fundamental skill set and a confidence in my abilities that will allow me to be successful in my career far beyond grad school. I would like to thank the committee members, Dr. Larry Hornak and Dr. Jeremy Dawson. Both of whom made themselves available and were always willing to help when I had questions. Specifically, Dr. Hornak's help in device design to suppress the electromagnetic feedthrough of the SAW devices and Dr. Dawson's help in optimizing the fabrication processes in the cleanroom.