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

Abstract

Total-ionizing-dose effects in AlGaN/GaN 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(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) under different bias conditions. Irradiated devices show significant electrical shifts in threshold voltage and transconductance. At doses <10 Mrad(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ), the TID-induced effects are related to the passivation of pre-existing acceptor-like defects via hole capture, which induces negative threshold voltage shifts and improvement of transconductance. At doses >10 Mrad(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ), 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.