| AlGaN/GaN high electron mobility transistors are unique for their combination of high temperature, high power, and high frequency applications. Compared to Si, Ge, and compound semiconductors such as GaAS and InP, AlGaN/GaN transistors outclass the current technology due to their superior combination of high breakdown voltage and high frequency performance. These characteristics arise from structural and electrical properties inherent to the AlGaN/GaN heterojunction which have enabled AlGaN/GaN transistors usage in important military and civilian applications such as microwave and millimeter technology, RADAR systems, and as high current and voltage switches in utility grid systems. As the technology continues to improve due to increased materials quality and device advancements, future applications will require AlGaN/GaN transistor usage under even higher voltages and temperatures. Therefore, the effects of these stresses need to be investigated in order improve device performance and reliability.;When stress conditions are applied in combination, device failure is accelerated. However, future applications may require electrical or thermal stress to be effectively applied separately. Therefore, it is important to understand how each factor contributes individually to the reliability and failure mechanisms in transistors to determine the actual working device life-time in its operating environment. The following research employs structural, chemical, and electrical device characterization paired with simulation in order to develop structure-property relationships between defects and device performance.;Here, for the first time, as-grown gate interfacial layers were characterized using atom probe tomography and are composed of two distinct oxide layers, NiOx and AlOx. Knowing the composition permits elimination or reduction of the layers through etching or processing modifications. Furthermore, using off-state reverse bias electrical stress, Ni-gate metal reactions with AlGaN epilayers emulate the shape and size of the electric field contours between 5 -- 6 MV/cm; an advancement from the previous understanding that defects form only at the peak electric field. Finally, application of only thermal stress is shown for the first time to cause gate metal penetration into threading dislocations. This penetration combined with Ni-Au gate metal interdiffusion causes a negative shift in threshold voltage, an increase in drain current, and only above 400°C an increase in gate leakage. |
