Low-temperature characteristics of normally-off AlGaN/GaN-on-Si gate-recessed MOSHFETs

We investigated the low-temperature operation of normally-off AlGaN/GaN heterostructure field-effect-transistors (HFETs) with gate-recessed metal-oxidesemiconductor (MOS) structure and normally-on Schottky-gate high-electron-mobility-transistors (HEMTs). Device characteristics measured from 100 to 300 K exhibited the distinct temperature-dependence between two types of devices. While the increase of on-current was observed from normally-on AlGaN/GaN Schottky-gate HEMTs due to the enhanced mobility in the two-dimensional electron gas (2-DEG) channel, normally-off AlGaN/GaN gate-recessed MOSHFETs demonstrated distinctive characteristics at 100 K including the decrease of on-current and the positive shift of threshold voltage (Vth). The temperature-dependence observed in gate-recessed MOSHFETs is attributed to the different characteristics of the recessed channel from the 2-DEG channel, in which the sheet carrier density (nsh) and mobility (μ) were reduced as the temperature approaches the cryogenic regime.