Abstract
The thickness of the LPCVD-Si(3)N(4) gate dielectric layer significantly influences the electron transport properties of AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs), but the mechanism by which it affects polarization Coulomb field (PCF) scattering remains largely unexplored. In this study, AlGaN/GaN MIS-HEMTs with LPCVD-Si(3)N(4) gate dielectric thicknesses of 0 nm, 5 nm, and 20 nm were fabricated, and the influence of LPCVD-Si(3)N(4) thickness on PCF scattering was systematically investigated. Through electrical measurements and theoretical calculations, the relationship between LPCVD-Si(3)N(4) gate dielectric layer thickness, additional polarization charge (∆ρ), two-dimensional electron gas (2DEG) density, and 2DEG mobility was analyzed. The results show that increasing the LPCVD-Si(3)N(4) thickness reduces the vertical electric field in the AlGaN barrier, weakening the inverse piezoelectric effect (IPE) and reducing ∆ρ. Further analysis reveals that the ∆ρ exhibits a non-monotonic dependence on negative gate voltage, initially increasing and subsequently decreasing, due to the competition between strain accumulation and stress relaxation. Meanwhile, the 2DEG mobility limited by PCF (μ(PCF)) decreases monotonically with increasing negative gate voltage, mainly due to the progressive weakening of the 2DEG screening effect. The research results reveal the physical mechanism by which LPCVD-Si(3)N(4) thickness regulates PCF scattering, providing theoretical guidance for optimizing gate dielectric parameters and enhancing the performance of AlGaN/GaN MIS-HEMTs.