Date of Award
Master of Science
Department of Engineering Physics
John W. McClory, PhD
AlxGa1-xN/GaN Heterostructure Field Effect Transistors (HFETs) have come under increased study, in recent years, owing to their highly desirable material and electrical properties, ruggedness, and survivability even during and after exposure to extreme temperature and radiation environments. These devices or similar devices constructed of AlGaN and/or GaN materials are being researched for their potential applications in many military and space based systems. In this study, unpassivated and SiN passivated Al0.27Ga0.73N/GaN HFETs were subjected to electron radiation at incident energies of 0.5MeV and 1.0MeV and fluences from 5x1014 to 5x1015 [e-/cm2] while maintained in a 10-6 Torr or higher vacuum at liquid nitrogen temperature (LN). The primary focus of the research was the effects of electron radiation and temperature on drain current, gate leakage current, threshold voltage shift, and gate-channel capacitance. Measurements were taken of transistor current, gate-channel capacitance, and gate leakage current vs. gate bias at 4°K temperature intervals beginning at LN through room temperature (RT). The resulting gate leakage currents were fitted to a Trap-Assisted Tunneling model and transistor currents were compared to a Charge Control model to evaluate post-irradiation change mechanisms to the parameters of these models. Post-irradiation drain currents increased for all devices, with a consistently lesser increase observed for passivated devices. Most post-irradiation increases returned to nearly pre-irradiation levels after an RT anneal period. Threshold voltage shifts averaged -0.5V for unpassivated and -0.2V for passivated HFETs, showed negligible temperature dependence, and returned to near pre-irradiation values, after RT anneal periods. Gate leakage currents showed post-irradiation increases for all devices.
DTIC Accession Number
Moran, Jeffrey T., "The Effects of Temperature and Electron Radiation on the Electrical Properties of AlGaN/GaN Heterostructure Field Effect Transistors" (2009). Theses and Dissertations. 2453.