Operational frequency degradation induced trapping in scaled GaN HEMTs

Abstract

Cut-off frequency increase from 12.1GHz to 26.4GHz, 52.1GHz and 91.4GHz is observed when the 1μm gate length GaN HEMT is laterally scaled down to LG=0.5μm, LG=0.25μm and LG=0.125μm, respectively. The study is based on accurately calibrated transfer characteristics (ID-VGS) of the 1μm gate length device using Silvaco TCAD. If the scaling is also performed horizontally, proportionally to the lateral (full scaling), the maximum drain current is reduced by 38.2% when the gate-to-channel separation scales from 33nm to 8.25nm. Degradation of the RF performance of a GaN HEMT due to the electric field induced acceptor traps experienced under a high electrical stress is found to be about 8% for 1μm gate length device. The degradation of scaled HEMTs reduces to 3.5% and 7.3% for the 0.25μm and 0.125 gate length devices, respectively. The traps at energy level of ET=EV+0.9eV (carbon) with concentrations of NIT=5×1016cm−3, NIT=5×1017cm−3 and NIT=5×1018cm−3 are located in the drain access region where highest electrical field is expected. The effect of traps on the cut-off frequency is reduced for devices with shorter gate lengths down to 0.125μm.