Achievement of normally-off AlGaN/GaN high-electron mobility transistor with p-NiOx capping layer by sputtering and post-annealing

•A technique to fabricate normally off GaN-based high-electron mobility transistor (HEMT) by sputtering and post-annealing p-NiOx capping layer.•The Vth shifts from −3V in the conventional transistor to 0.33V, and on/off current ratio became 107.•The reverse gate leakage current is 10−9A/mm, and the off-state drain-leakage current is 10−8A/mm.•The Vth hysteresis is extremely small at about 33mV.