Simulation of in situ reflectance-time during MOVPE of GaN on sapphire substrate

Abstract

An optical model incorporating time-dependent surface roughness and time-dependent growth rate was used to simulate the in situ reflectance-time during the metalorganic vapor phase epitaxy (MOVPE) of GaN on sapphire substrate. Excellent fits to experimental data have been obtained and leaded to determine the high temperature GaN optical constants and both profiles of surface roughness and growth rate during the transient from three-dimensional (3D) to two-dimensional (2D) growth modes. From simulation, recovery time (τr), thickness and surface roughness are extracted. The results show that the growth rate increases to reach a limit value when 2D growth mode is established. At the same time, surface roughness decreases from a high value (65–75nm) to lower than 10nm if the growth is ended by 2D mode. In the case of surface smoothing is followed by surface degradation, a sum of two surface roughness profiles was suggested and given good simulation results. In this case, the reflectivity damping is characterized by new time constant so called damping time (τd) that also considered as fit parameter. Several in situ reflectivity traces corresponding to different growth conditions are chosen for these simulations. High temperature GaN refractive index extracted from simulations are close to those reported in the literature. The output simulations are correlated with ex situ analyses by UV–Visible transmission and Hall Effect that showed good accordance.