Quantitative study of nitridated sapphire surfaces by x-ray photoelectron spectroscopy

Abstract

The characteristics of an amorphous oxynitride layer formed by nitridation are studied with x-ray photoelectron spectroscopy in order to reveal the role of nitridation before GaN growth in metalorganic chemical vapor deposition. The intensity variation of the N 1s peak with nitridation time is analyzed quantitatively using a diffusion-based model. The effective diffusion coefficient of nitrogen-related species in the amorphous layer is estimated to be 4×10−18 cm2/s at 1000 °C. The thickness of the amorphous layer is on the order of monolayers because of this small diffusion coefficient. The nitrogen concentration in the layer, however, is as high as the order of the site density of O atoms on the sapphire surface. These characteristics imply that the role of the amorphous layer formed by nitridation is to modify surface energy with high-density N atoms rather than to form a buffer-like layer.