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

摘要

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 °C in N₂ 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 $2.1imes 10^{7}$ . 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.