# Influence of LPCVD-Si3N4 Thickness on Polarization Coulomb Field Scattering in AlGaN/GaN Metal–Insulator–Semiconductor High-Electron-Mobility Transistors

## TL;DR

This paper explores how the thickness of a gate dielectric layer affects electron mobility in AlGaN/GaN transistors by influencing polarization charge and electric fields.

## Contribution

The study reveals the physical mechanism linking LPCVD-Si3N4 thickness to polarization Coulomb field scattering in AlGaN/GaN MIS-HEMTs.

## Key findings

- Increasing LPCVD-Si3N4 thickness reduces vertical electric field and polarization charge in the AlGaN barrier.
- Polarization charge shows non-monotonic behavior with gate voltage due to strain and stress effects.
- 2DEG mobility decreases with negative gate voltage due to weakened screening effect.

## Abstract

The thickness of the LPCVD-Si3N4 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-Si3N4 gate dielectric thicknesses of 0 nm, 5 nm, and 20 nm were fabricated, and the influence of LPCVD-Si3N4 thickness on PCF scattering was systematically investigated. Through electrical measurements and theoretical calculations, the relationship between LPCVD-Si3N4 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-Si3N4 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 (μPCF) 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-Si3N4 thickness regulates PCF scattering, providing theoretical guidance for optimizing gate dielectric parameters and enhancing the performance of AlGaN/GaN MIS-HEMTs.