E-mode AlGaN/GaN HEMTs using p-NiO gates

Sputtered p-NiO films were used to suppress gate leakage and produce a positive shift in the gate voltage of AlGaN/GaN high-electron mobility transistors for e-mode operation. A direct comparison with Schottky-gated devices fabricated on the same wafer shows the utility of the NiO in increasing the on-off ratio and shifting the threshold voltage from −0.95 V (Schottky gated) to +0.9 V (NiO gated). The breakdown voltage was 780 V for a 40 μm drain-source separation. The subthreshold swing decreased from 181 mV/dec for Schottky-gated HEMTs to 128 mV/dec on NiO-gated devices. The simple fabrication process without any annealing or passivation steps shows the promise of NiO gates for e-mode AlGaN/GaN HEMT operation.