Improved Interface Quality and Stability of AlGaN/GaN Metal–Insulator–Semiconductor High-Electron-Mobility Transistors Using N ₂ -Annealed Atomic-Layer-Deposited SiN x Gate Dielectrics

GaN-based metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) are pivotal for next-generation power electronics due to their high breakdown voltage, low gate leakage current, and reliable operation stability compared with HEMT devices. The lack of high-quality native oxides necessitates a rigorous evaluation of gate dielectrics. Atomic-layer-deposited (ALD)-SiNx emerges as a promising candidate that enables superior device characteristics. However, defects at the ALD-SiNx/(Al)GaN interface or in the ALD-SiNx bulk, such as silicon or nitrogen dangling bonds, can induce charge trapping/detrapping under bias, leading to threshold voltage (VTH) instability and dynamic ON-resistance (RON) degradation. This study systematically investigates defect evolution at the ALD-SiNx/(Al)GaN interface and within the dielectric layer using X-ray photoelectron spectroscopy (XPS) and deep-level transient spectroscopy (DLTS). Correlating the postdeposition annealing (PDA) treatments with specific defect revolution reveals the underlying mechanisms governing device performance. Results demonstrate that N₂ annealing (550 °C, 5 min) achieves suppressed interface state density without compromising dielectric quality, whereas oxygen-containing annealing introduces thermally aggravated bulk defects despite partial interface improvement. Benefiting from the optimized N₂-based annealing strategy, the fabricated AlGaN/GaN MIS-HEMTs exhibit significantly enhanced performance metrics: suppressed VTH hysteresis, steep subthreshold swing (SS), stable dynamic RON, and robust threshold voltage stability. These results highlight the critical role of defect control in ALD-SiNx dielectrics, particularly through N₂ annealing-induced suppression of deep-level interface states, thereby providing a practical strategy to enhance the interface quality and electrical performance of AlGaN/GaN MIS-HEMTs.