Assessment of refractive index changes by spectral reflectance in the first stages of AlxGa1−xN layer growth using SiN treatment

Abstract

AlxGa1−xN films were grown using SiN treatment of sapphire substrate by metalorganic vapor phase epitaxy in a home-made vertical reactor. AlxGa1−xN layer growth process was interrupted at successively steps to systematically investigate the first stages of AlxGa1−xN layer growth. The growth process is monitored using real time in situ normal incident laser reflectance at wavelength λ = 632.8 nm. We have developed a semi-empirical optical model based on effective medium approach that takes account of an evolving interface roughness of a multilayer film structure during the growth process. The optical model along with an efficient least square fitting procedure are implemented in a computer program to extract the refractive index changes of the AlxGa1−xN film structure from fitting ex situ multi-wavelength reflectivity signals at the transitional 3D–2D growth mode. Spectroscopic ellipsometry measurements are used to compare to refractive index predicted by this modelling. The simulation of in situ normal incident reflectivity signal is accurately achieved. Moreover, the reflectivity signal is fitted so as to extract the refractive index evolution during spontaneous cooling phase. The comparison between experimental results to those obtained from simulations corroborates the validity of the proposed approach in the case of similar conditions as those used in the present study.