Book Description

Throughout space, nuclear, and defense applications, electronics are subjected to radiation harsh environments. Gallium Nitride (GaN) is a promising material for such harsh environment applications because of its strong bonding, in addition to its favorable material properties for making electronic devices: wide bandgap, and high electron mobility. To qualify GaN for harsh environment applications, testing is required, including the need to assess GaN's hardness to total ionizing dose (TID) effects such as those from gamma radiation. One of the reasons for studying TID effects in GaN is that gamma radiation is present in many manmade radiation environments, and an additional reason for studying TID effects is that the secondary electrons from gamma radiation are a good way to simulate radiation damage from electrons accumulated during space missions, particularly in the Van Allen Belts. Throughout many of the studies on TID effects, results are highly varied, owing to variations in gate structure, radiation bias conditions, and material growth techniques, each of which are not always fully detailed in some reports. Because of the variation in present reports on TID effects in GaN, additional research into TID effects of GaN is needed before it can be confidently used in radiation-harsh environments. A comprehensive study of gamma radiation effects on commercial GaN devices is proposed in this work. Commercial devices from several manufacturers: an RF device, a pGaN/Schottky gate power device, and a p-GaN/Ohmic gate power device, each representative of their class are electrically characterized before, during, and after exposure to doses of gamma radiation from a Cobalt 60 (60Co) source under varying bias conditions. Transistor output and transfer characteristics are collected as well as drain and gate leakage current, dynamic on resistance, capacitance between drain and source (Cds), and between gate and source (Cgs), to comprehensively assess any degradation in the devices from an electrical standpoint. RF devices iv showed a slight negative threshold voltage shift post-irradiation under all bias conditions and an increase in gate and drain current during irradiation. P-GaN/Schottky gate power devices showed an increase in gate leakage in both on- and off-state post-irradiation and an increase in drain current during irradiation as well as a linearly increasing in-situ gate current with dose in offstate. p-GaN/Ohmic gate power devices showed no significant change. Findings are further explored by simulations, using several potential radiation models. Simulation results did not exactly match experimental findings, but they provide a first step in understanding more about the radiation response of these devices.