Improving Current ON/OFF Ratio and Subthreshold Swing of Schottky-Gate AlGaN/GaN HEMTs by Postmetallization Annealing

Al2O3-passivated Schottky-gate AlGaN/GaN high electron mobility transistors (HEMTs) with improved subthreshold swing (SS) and drain current ON/OFF ratio by postmetallization annealing (PMA) at 500 degrees C in N-2 ambient are reported. With the PMA, the gate leakage current in the reverse biased region and the OFF-state drain current are reduced by more than three orders of magnitude, leading to a low SS of 84.75 mV/dec and a high drain current ON/OFF ratio of 2.1 x 10(7). Through temperature-dependent current-voltage measurements on dual-Schottky-gate structures and capacitance-voltage measurements on Al2O3/AlGaN/GaN metal-insulator-semiconductor (MIS) HEMT capacitors, it is identified that the PMA greatly suppresses both the Al2O3/AlGaN interface leakage current and the reverse gate leakage current by eliminating Al2O3/AlGaN interface trap states with 0.34 eV trap state energy and changing the dominant mechanism of reverse gate leakage conduction from trap-assisted tunneling to Fowler-Nordheim tunneling, respectively. Overall, this work reports on the effectiveness of PMA in improving the performance of Schottky-gate AlGaN/GaN HEMTs and the underlying improving mechanisms.