Investigation into the growth mode of GaN thin films on 4H–SiC substrates via plasma-enhanced atomic layer deposition

Abstract

GaN ultra-thin films are deposited on 4H–SiC substrates using plasma-enhanced atomic layer deposition (PEALD). Our investigation reveals a remarkably narrow temperature window (225–275 °C) for GaN PEALD growth, characterized by substrate hindered nucleation retardation. Within this temperature window, the growth process exhibits three distinct stages, which are demarcated by the 35th and 200th cycles, each displaying unique characteristic, especially in aspects growth rate, film strain, surface topography, and crystallization. Notably, the instantaneous growth rate, which is often overlooked, provided a better representation of the growth state compared with growth per cycle (GPC) and shows better consistency with film strain and surface roughness. Additionally, we observed a step filling effect during the early stages (10 cycles) of ALD growth, which reduces surface roughness to 0.12 nm form 0.20 nm of substrate SiC. X-ray photoelectron spectroscopy (XPS) analysis reveals the formation of N–Si and N–C bonds on the sample surface following 20 cycles of plasma bombardment. Further analysis using high-resolution X-ray diffraction (HRXRD) and high-resolution transmission electron microscopy (HRTEM) consistently confirms the presence of a hexagonal wurtzite crystalline structure in GaN films deposited under varying cycle counts.