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This work demonstrates the robust single-event irradiation hardness in 650-V E-mode p-GaN HEMTs with source-connected buried metal structure. Such device design notably contributes to the removal of irradiation-induced holes accumulated in the reverse-biased p-GaN/ AlGaN/GaN (p-i-n) junction region, thereby improving irradiation robustness against single-event burnout (SEB). The resulting device exhibits significantly improved SEB voltages of 558 and 467 V under heavy ion linear energy transfer ( $LET_{\text {ion}}$ ) conditions of 75.7 and 86.3 MeV $\cdot $ cm2/mg, respectively, setting a new performance record for GaN-based power devices. Moreover, based on pulsed laser equivalent heavy ion irradiation system configured with a power switching circuit, a high power conversion efficiency of 95% is demonstrated under 77.6 LET PL, 300 W/500 kHz conditions. This work thus makes a significant step toward reaching the promise of GaN devices for radiation applications.

Highly stable threshold voltage $({V}_{\text {TH}})$ characteristics are an essential reliability requirement for p -GaN/AlGaN/GaN high-electron-mobility transistors (p-GaN HEMTs) to withstand various gate bias stresses for power applications. In this work, we demonstrate high- ${V}_{\text {TH}}$ (3.0 V) p-GaN HEMTs with robust ${V}_{\text {TH}}$ stability by p -GaN gate engineering via Mg doping and activation. The ${V}_{\text {TH}}$ degradation rates of the resulting device under both pulsed- ${I}/{V}$ and bias temperature instability (BTI) stress conditions are less than 10% at high temperatures up to 150°, which is much lower than that of conventional Schottky-type p -GaN HEMTs (20%–30%). Such notable ${V}_{\text {TH}}$ characteristics are due to the impact ionization (I.I.)-dependent hole compensation under certain gate stress, which effectively alleviates the electron trapping effect and reduces positive ${V}_{\text {TH}}$ shift. The I.I. occurring in the fully depleted p -GaN layer has been confirmed by both positive temperature-dependent gate breakdown characteristics and numerical simulations. Furthermore, shallow- and deep-level hole traps are identified in the gate-stack of high- ${V}_{\text {TH}}$ devices by performing the deep-level transient spectroscopy (DLTS) technique. Consequently, the trapping effect associated with hole traps may also alleviate the undesired electron-trapping-induced ${V}_{\text {TH}}$ shift. These results provide a critical understanding of the ${V}_{\text {TH}}$ stability of the high- ${V}_{\text {TH}}$ p -GaN HEMTs (HVT-HEMTs) and important design guidance for commercial device development.