Gate-Induced Threshold Voltage Instabilities in p-Gate GaN HEMTs

In this study, we investigate the threshold voltage (V-th) instability of p-gate GaN HEMTs induced by gate bias. Experimental results are acquired by a custom pulse setup for two commercially available devices with an ohmic gate and a Schottky gate. A transient drain current change is observed, which corresponds to a shift of V-th. A negative Vth instability is identified for the ohmic gate, amostly positive for the Schottky gate that can also become negative depending on the gate bias voltage and duration. The impact of the gate-bias-induced V-th instability on the Schottky-gate device is significantly higher compared to the ohmic-gate device, but clearly noticeable at the nominal rated ON-state gate voltage for both devices. Electron depletion and trapping as well as hole accumulation and trapping are identified to cause this transient V-th instability.