SUMMARY

Gallium Nitride (GaN) has been targeted for use in high power (>30W/mm) and high frequency (>160GHz) applications due to its wide band gap and its large break down field. One of the most significant advances in GaN devices has evolved from the AlGaN/GaN high electron mobility transistor (HEMT). Technologies that incorporate such devices span the range from next generation WiMAX stations to advanced military radar applications. As a result of the large power densities being applied to these devices there can develop intense hot spots near areas of highest electric field. The hot spot phenomenon has been linked to a decrease in device reliability through a range of degradation mechanisms. In order to minimize the effect that hot spot temperatures have on device reliability a detailed understanding of relevant transport mechanisms must be developed. This study focuses on two main aspects of phonon transport within GaN devices. The first area of focus was to establish an understanding of phonon relaxation times within bulk GaN. These relaxation times were calculated from an application of Fermi’s Golden Rule and explicitly conserve energy and crystal momentum. Relaxation times for optical modes were compared to experimental data obtain through Raman Spectroscopy linewidth measurements. Acoustic phonon relaxation times were calculated in order to capture the bulk thermal conductivity values of GaN. This analysis gives insight into the details behind the macroscopic thermal conductivity parameter. Once relaxation times for GaN were established a multiscale phonon transport modeling methodology was developed that allowed the Boltzmann Transport Equation to be coupled to the Energy Equation. This coupling overcomes some computational limits and allows for nanoscale phenomena to be resolved within a macroscopic domain. Results of the transport modeling were focused on benchmarking the coupling method as well as calculating the temperature distribution within an operating 6 finger HEMT.