Investigation on shift in threshold voltages of 1.2 kV GaN polarization superjunction (PSJ) HFETs

Shift in threshold voltages ( Vth ) of 1.2 kV P-GaN ohmic-gate normally- ON polarization superjunction (PSJ) HFETs is reported for the first time. Pulsed-mode measurement results of threshold voltage shifts under different gate stress biases are presented. A comprehensive analysis of threshold voltage shifts under different gate stress voltages and temperatures is discussed. Under positive gate stress voltages, hole trapping and accumulation processes in the u-GaN/AlGaN hetero-interface or the AlGaN layer induce more electrons, thereby causing negative shifts in threshold voltages. Conversely, under negative gate stress voltages, electrons captured by the buffer traps located in the GaN buffer or the traps in the AlGaN layer cause positive shifts in threshold voltages. Moreover, recovery processes are observed under the positive and negative stress voltages. Temperature effects on the Vth are also evaluated through pulsed-mode measurements. Hole trapping processes are strengthened with temperature rise, causing more negative Vth shifts. However, thermally activated electrons from 2DEG and strengthened recovery processes result in positive Vth shifts at higher temperatures, compensating the influences from the increasing hole trapping processes. The results confirm that the current collapse is quite low in PSJ HFETs