(Invited) Electrothermal Performance Optimization of III-Nitride HEMTs Capped with Nanocrystalline Diamond

Abstract

AlGaN/GaN high electron mobility transistors (HEMT) capped with nanocrystalline diamond (NCD) have been demonstrated in the past to outperform electrically and thermally their SiN-passivated counterparts. However, a major process limitation for the integration of a diamond heat spreader has been the O2-plasma damage in the gate opening associated with etching the diamond cap. A sacrificial gate (SG) process for plasma damage-free integration of top-side NCD capping layers is thus developed. On HEMTs with a SG, the addition of a NCD cap did not cause any significant degradation in mobility, carrier density, or sheet resistance. Hall characterization showed minimal (~6%) reduction in sheet carrier density and commensurate increase in sheet resistance, while maintaining mobility and on-state drain current density. Pulsed IDS and on-resistance were improved, indicating that a 10 nm SiN/500 nm NCD could offer improved AlGaN surface passivation compared to a more conventional 100 nm thick PECVD SiN film.