Investigations of in situ reflectance of GaN layers grown by MOVPE on GaAs (0 0 1)

• Significant change from 2D to 3D growth of GaN on GaAs (0 0 1) was obtained in tight domain of growth temperature (500–600 °C).
• Quantitative optical model yields to extract the surface roughness and growth rate profiles.
• High density of nucleation sites was found suitable to improve the GaN quality grown at 800 °C.

The growth of low temperature GaN (LT-GaN) layers on GaAs (0 0 1) substrate was performed by metal organic vapor phase epitaxy (MOVPE) at growth temperature range of 500–800 °C. Laser reflectometry (LR) was employed for in situ monitoring of all growth steps. The simulation of experimental time reflectance traces shows that at the first growth stage, the surface roughness increases to reach a limit value depending on growth temperature. Due to surface roughness profile the growth rate time-dependence was found non negligible at the first growth stage. The investigations of in situ reflectance give more precise measurement of growth rates that yields to thermal activation energy close to 0.12 eV. The ex-situ analyses by spectral reflectance (SR) and Atomic Force Microscopy (AFM) showed that the better surface morphology was obtained when the GaN buffer layer is grown at lower temperature, while three dimensional (3D) growth mode was observed at higher temperature. A series of high temperature (800 °C) GaN (HT-GaN) layers were grown on different thicknesses of low temperature (550 °C) GaN buffer layer. The results showed that high density of nucleation sites enhances the initial growth rate and improves the morphological quality of GaN active layer.