In-situ monitoring of GaN MOVPE by shallow-angle reflectance using ultraviolet light

The surface flatness of GaN grown by metalorganic vapor phase epitaxy (MOVPE) on c-plane sapphire substrates was monitored in situ by shallow-angle reflectance using p-polarized ultra-violet light (325 nm). During low-temperature GaN (LT-GaN) buffer growth at 600 degrees C, an oscillation due to an optical interference was observed, indicating the thickness can be controlled in situ to a few nm accuracy. During GaN growth at 1050 degrees C on LT-GaN, clear oscillations and no decrease of reflectivity indicate that the growth proceeds smoothly within a roughness of 10 nm. When both the surface roughness and hexagon density on the surface increased, the oscillation was quickly damped and the reflectivity decreased monotonously. The decrease in reflectivity is proportional to the product of the surface roughness and hexagon density. These results indicate that this method is a powerful tool for monitoring in situ the surface flatness and also for optimizing growth parameters, which are interrelated in GaN MOVPE. (C) 1998 Elsevier Science B.V. All rights reserved.