High-reliability normally off AlGaN/GaN HEMTs with a 720 V breakdown voltage via a TCAD-optimized GaN cap layer

Abstract This work presents a detailed Technology Computer Aided Design (TCAD) and Transport of Ions in Matter (TRIM)-based simulation study of normally off AlGaN/GaN high-electron-mobility transistors (HEMTs), focusing on the influence of the thickness of the GaN cap layer on device performance. The study evaluates threshold voltage modulation through nitrogen ion implantation across cap thicknesses of 0 , 1 , and 2 nm. The 2 nm cap configuration yielded optimal results, including a breakdown voltage of 720 V, a drain current density of 1.45 × 10 −2 A mm −1 , a gate leakage current of 5.35 × 10 −11 A mm −1 , and a positive threshold voltage of 0.366 V. TRIM simulations confirmed that the cap layer significantly affects nitrogen ion distribution and damage profiles, influencing two-dimensional electron gas formation. Schottky barrier height variations were also observed, correlating with cap-induced modulation of the surface potential. Although converter-level efficiency is influenced by passives, parasitics, and control strategies, our device-level results indicate that cap-optimized HEMTs can enable high-efficiency operation in MHz-class buck converters. These findings underscore the effectiveness of GaN cap-layer engineering in strengthening the breakdown, improving the gate control, and enhancing overall enhancement-mode GaN HEMT performance.