SUMMARY

Possessing a wide band gap and large break down field, gallium nitride (GaN) is of extreme interest for a host of high power, high frequency applications including next generation cellular base stations, advanced military radar, and WiMAX networks. Much of this interest stems from the continued development of the AlGaN/GaN high electron mobility transistor (HEMT) which is capable of operating at extravagant power densities and switching speeds. The same fields responsible for this performance, however, also elicit acute device heating and elastic loads. These induced thermomechanical loads, meanwhile, limit both performance and reliability thus necessitating continued improvement in the management and characterization of the coupled environments. In response, this study establishes a new implementation of Raman spectroscopy to investigate the thermal and mechanical burdens present in GaN devices while in operation. First, the linewidth (FWHM) of the Stokes signal is utilized to measure the operating temperature of a HEMT independent to the influences of operational thermoelastic stress. Second, a new method incorporating multiple aspects of the Raman spectrum is then developed to observe the evolution of this stress in order that the full mechanical response, and its dependence to device substrate, may be quantified for the first time. This same linewidth is then leveraged to examine the underlying physics of thermal energy transfer which gave rise to the previously measured values through investigation of the effect of free carriers on phonon transport. Further investigation of the lattice transport then concludes the study by way of an analytical treatment to the role of interfacial disorder on the energy transport at GaN/substrate boundaries.