Performance Improvement in AlGaN/GaN High‐Electron‐Mobility Transistors by Low‐Temperature Inductively Coupled Plasma–Chemical Vapor Deposited SiNx as Gate Dielectric and Surface Passivation

Abstract

This work demonstrates performance improvements in AlGaN/GaN metal–insulator–semiconductor high‐electron‐mobility transistors (MIS‐HEMTs) using low‐temperature inductively coupled plasma chemical vapor deposited (ICP–CVD) silicon nitride (SiN x ). The low‐temperature SiN x is used for both device passivation and gate dielectric. The bandgap of SiN x (4.9 eV) and AlGaN/SiN x type‐II staggered band alignment (ΔE c = 1.4 eV) are determined using ultraviolet‐visible spectroscopy and ultraviolet photoelectron spectroscopy, respectively. The SiN x layer effectively increases the in‐plane tensile strain in the AlGaN barrier layer. The tensile strain increases by 0.08% for a 150 nm SiN x layer. The corresponding increase in the piezoelectric polarization and 2D electron gas (2DEG) density is 1.5 × 1012 and 1.44 × 1012 cm−2, respectively. The transistor's on‐resistance decreases to 9.33 Ω mm compared with 14 Ω mm measured for the control devices with gate length 1 μm and source and drain separation of 11 μm. The gate leakage current reduces by more than three orders of magnitude. The I ON/I OFF ratio increases by two orders of magnitude. The improvements in the physical and electrical properties of the low‐temperature‐deposited ICP–CVD SiN x MIS‐HEMTs make it a viable candidate for low‐thermal‐budget fabrication. This nitride can be used with non‐alloyed Ohmic contacts on GaN for extremely low‐thermal‐budget transistors.