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)-SiN x emerges as a promising candidate that enables superior device characteristics. However, defects at the ALD-SiN x /(Al)GaN interface or in the ALD-SiN x bulk, such as silicon or nitrogen dangling bonds, can induce charge trapping/detrapping under bias, leading to threshold voltage ( V TH ) instability and dynamic ON-resistance ( R ON ) degradation. This study systematically investigates defect evolution at the ALD-SiN x /(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 N 2 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 N 2 -based annealing strategy, the fabricated AlGaN/GaN MIS-HEMTs exhibit significantly enhanced performance metrics: suppressed V TH hysteresis, steep subthreshold swing (SS), stable dynamic R ON, and robust threshold voltage stability. These results highlight the critical role of defect control in ALD-SiN x dielectrics, particularly through N 2 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.