Improved Stability of Fully Recessed Normally-Off GaN MIS-HEMTs With SiNx/AlN Dielectric Stack

This work presents a comparative study of GaN metal-insulator-semiconductor high-electron-mobility-transistors (MIS-HEMTs) employing LPCVD-SiNx/ALD-AlN or PEALD-SiO2/ALD-AlN dielectric stacks. The SiNx/AlN MIS-HEMTs exhibit a minimal threshold voltage shift ( $\Delta {V}_{\text {TH}}$ ) of −0.24 V with an on/off current ratio up to $10^{{8}}$ under $150~^{\circ }$ C, compared to $\Delta {V}_{\text {TH}}=2.0$ V for SiO2/AlN MIS-HEMTs. Under gate bias stress, SiNx/AlN devices show $\Delta {V}_{\text {TH}}$ of −0.90 V (positive) and −0.45 V (negative), versus −1.75 and 3.31 V for SiO2/AlN devices. After maintaining $10^{{4}}$ s of off-state drain-bias stress, SiNx/AlN MIS-HEMT achieves a small $\Delta {V}_{\text {TH}}$ of −0.45 V. The improved stability is attributed to the better interface quality of SiNx/AlN stack, enabled by the low-pressure chemical vapor deposition (LPCVD) process and nitrogen-rich environment. These findings underscore the potential of LPCVD-SiNx/ALD-AlN dielectric stacks in advancing GaN MIS-HEMTs for high-performance and reliable power switching applications.