Normally-off GaN MOSFETs on insulating substrate

Several types of GaN MOSFETs with normally-off operation have been fabricated on insulating substrate and evaluated. In recessed-gate GaN MOSFET, the threshold voltage (V_th) can be easily controlled, but the current drivability is modest and needs to be improved by adopting appropriate device structure and/or process. We achieved enhanced performance by combining the recessed-gate technology with additional processes, such as: (i) the post-recess tetramethylammonium hydroxide (TMAH) treatment to remove the plasma damage, (ii) the post-deposition annealing of gate oxide to decrease the gate leakage current, (iii) the re-growth of n⁺-GaN layer for source/drain to improve the access resistance and V_th uniformity, (iv) the stress-control technology to secure high 2-D electron-gas density (2DEG) on source/drain and decrease the series resistance, and (v) the use of the p-GaN back-barrier to decrease the buffer leakage current. We also present the characteristics of GaN-based FinFETs with very narrow fin.