Total-Ionizing-Dose Effects at Ultrahigh Doses in AlGaN/GaN HEMTs

Total-ionizing-dose (TID) effects in AlGaN/GaN high-electron-mobility transistors (HEMTs) are evaluated by dc and low-frequency noise measurements. Devices with and without passivation layers are irradiated with 10-keV X-rays up to 100 Mrad(SiO2) under different bias conditions. Irradiated devices show significant electrical shifts in threshold voltage and transconductance. At doses < 10 Mrad(SiO2), the TID-induced effects are related to the passivation of preexisting acceptor-like defects via hole capture, which induces negative threshold voltage shifts and improvement of transconductance. At doses
$>$
10 Mrad(SiO2), dehydrogenation of defects and impurity complexes leads to the creation of acceptor-like defects, which degrade the transconductance, shift positively the threshold voltage, and increase the low-frequency noise. Effects are enhanced in unpassivated devices and when the gate is biased at high voltage.