This work investigates the influence of gate metal selection on the gate leakage current of AlGaN/GaN high-electron-mobility transistors (HEMTs) through a systematic temperature-dependent analysis in the range of 238.5–473.15 K. A direct comparison between different gate-metal/process configurations characterized under the same measurement conditions is performed to clarify their impact on leakage mechanisms. The results reveal a transition between dominant conduction mechanisms as a function of temperature, electric field, and gate stack properties. At low temperatures and electric fields, the leakage current is mainly governed by tunneling-related processes, while thermally activated mechanisms become increasingly significant as temperature increases. Under high electric field conditions, the observed trend is consistent with Fowler–Nordheim tunneling. A semi-logarithmic analysis of ln (IG) as a function of inverse temperature shows the absence of a well-defined Arrhenius behavior, indicating that the leakage current is not dominated by a single thermally activated mechanism. Instead, the weak temperature dependence observed in several regimes suggests a strong contribution of tunneling-related transport, with additional mechanisms becoming relevant depending on the device structure and bias conditions. The results demonstrate that the transition between conduction mechanisms occurs over different temperature ranges depending on the gate metal, highlighting the critical role of the metal–semiconductor interface in defining leakage behavior. These findings provide improved insight into leakage mechanisms in GaN-based devices and offer guidance for device design and reliability optimization.
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