High-Performance AlN/GaN HEMTs on Sapphire Substrate With an Oxidized Gate Insulator

This letter presents transistor device results on ultrathin AIN/GaN high-electron mobility transistors grown on a sapphire substrate with high dc/RF performance, including low gate leakage and high transconductance. Devices with 80and 180-nm T-gates are compared, which demonstrate drain-induced OFF-state gate leakage currents below 10^-6 A/mm and extrinsic transconductance g_m ~ 500 mS/mm by utilizing a ~2-3 nm amorphous oxide layer formed under the T-gate during processing. In addition, excellent dc results such as R_C <; 0.50 Ω · mm and pulsed I_DS,max ~1.75 A/mm are reported. Small-signal RF performance using an 80-nm T-gate achieved f_t >; 100 GHz operation, which is among the best so far reported for AIN/GaN technology.