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In this study, we investigate the threshold voltage (${V} _{{{ \text {th}}}}$) 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 ${V} _{{{ \text {th}}}}$. A negative ${V} _{{{ \text {th}}}}$ instability is identified for the ohmic gate, a mostly 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 ${V} _{{{ \text {th}}}}$ 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 ${V} _{{{ \text {th}}}}$ instability. [ABSTRACT FROM AUTHOR]

A study of electrical and thermal failure modes of 600 V p-doped GaN HEMTs is presented, which focuses on the investigation of short-circuit limitations. The electrical failure mode seems to be an electrical field breakdown in the structure which is caused by excessive carrier concentration, rather than primary thermal generated. Accordingly, a thermal failure mode is observed, which features a distinctive behaviour and seems to be similar to schottky-gate HEMTs. Concerning the electrical failure mode, a specific p-gate HEMT short-circuit safe operating area (SCSOA) is presented as a novelty. However, a short-circuit capability of up to 520 V can be achieved, regarding the design of the gate-drive circuit. [ABSTRACT FROM AUTHOR]