Suppression of Interface Traps and Improved Breakdown in Recessed-Gate AlGaN/GaN MISHEMTs Using Low-Temperature...

Recessed-gate AlGaN/GaN MISHEMTs are promising candidates for power electronics but often suffer from interface defects introduced during gate recessing, which degrade device performance and reliability. In this work, a supercritical fluid nitrogen passivation (SCFNP) technique is developed to address this limitation. The process is carried out at 180 °C under high pressure and enables efficient defect repair at both the Al₂O₃/AlGaN interface and the recessed-gate surface. Devices treated with SCFNP exhibited significantly improved electrical performance, including a positive threshold voltage (V _TH) shift to +2.2 V (extracted at I _D = 1 mA/mm), an increased maximum drain current of 600 mA/mm, a substantially reduced gate leakage current of 9.9 × 10^-8 mA/mm, and a high on/off current ratio of 5.0 × 10⁹. The gate leakage current decreased by nearly 2 orders of magnitude, while the OFF-state breakdown voltage (BV) increased by 27.8% (from 557 to 712 V). Dynamic on-resistance (R _ON) measurements further revealed a 25.6% reduction in current collapse under high-voltage stress. TCAD simulations corroborate these experimental results by demonstrating that reduced interface trap density suppresses peak electric fields at the drain edge, thereby validating the observed BV enhancement mechanism. Overall, SCFNP represents a low-temperature and scalable postfabrication passivation strategy for reliable GaN power devices.