Temperature-Dependent Electro-Thermal Characteristics of E-Mode GaN HEMTs with Ohmic and Schottky Gates

p-GaN gate enhancement-mode GaN HEMTs are promising normally-off power devices, but their high-temperature reliability is strongly affected by the gate contact scheme. This study compares Pd-ohmic and Ni-Schottky p-GaN gate HEMTs fabricated on the same GaN-on-Si epitaxial platform by combining temperature-dependent electrical characterization, post-temperature-dependent-test (TDT) room-temperature recovery analysis, and thermoreflectance thermal mapping. Electrical measurements were performed from room temperature to 500 °C using gate leakage, transfer, and output characteristics, while thermal maps were obtained before and after TDT under identical bias conditions. The Pd-ohmic devices exhibited higher initial current drive but larger operating gate-current penalty and stronger degradation of normalized on-state characteristics at elevated temperature. After TDT, reduced transconductance and maximum drain current were accompanied by weaker active-channel heating, indicating degradation-type cooling associated with reduced gate-channel modulation efficiency. In contrast, the Ni-Schottky devices showed lower gate-current penalty and better normalized output retention up to approximately 300 °C; however, post-TDT increases in transconductance and drain current occurred together with degraded subthreshold swing and persistent localized heating, indicating apparent on-state activation with weakened gate/depletion control. These results show that p-GaN gate reliability should be assessed through coupled electrical and thermal signatures rather than single electrical or thermal metrics.