Threshold Voltage Instability of Schottky-type p-GaN Gate HEMT down to Cryogenic Temperatures

The frozen trap effect can influence the threshold voltage of $p$-GaN gate HEMT when the temperature decreases to 15 K. The freezing of hole traps occurs at a higher temperature since their energy levels are deeper than that of electron traps, leading to a turning point of the threshold voltage and gate capacitance depending on temperatures. A high gate bias facilitates the emission of frozen carriers, which has a barrier-lowering effect, counteracting the frozen trap effect. At cryogenic temperatures, the threshold voltage of $p$-GaN gate HEMT becomes stable after long-time gate stress, showing promising potential for cryogenic applications.