Observation of trap-assisted steep sub-threshold swing in schottky source/drain Al2O3/InAlN/GaN MISHEMT

Devices with steep subthreshold swing (SS) are of great interest and significance in view of increasing subthreshold leakage current with the continuous MOSFET scaling. The standby power dissipation has grown due to the nonscalability of the SS to below 60 mV/dec at room temperature (RT). To circumvent this obstacle, novel devices that employ various turn-on mechanisms have been proposed1–4. In this work, we report the observation of steep SS∼20 mV/dec in Schottky source/drain (SSD) Al2O3/InAlN/GaN MIS-HEMTs over a drain bias range of 0.1 to 5 V. The devices also feature high ION/IOFF ratio (∼109) and appreciable current drive of IDmax=230 mA/mm at room temperature. The devices are also characterized at elevated temperature (T) up to 155 °C. Steep SS lower than the theoretical diffusion limit is consistently observed over the testing temperature range. It is suggested that the steep switching behavior is obtained through the means of a dynamic de-trapping process at the Al2O3/InAlN interface. The dynamic de-trapping enables a dynamic negative shift in the threshold voltage during the gate upswing and effectively facilitates the formation of a sub-threshold swing as steep as 18 mV/dec.