Influence of Al<inf>x</inf>Ga<inf>1-x</inf>N nucleation layers on MOVPE-grown zincblende GaN epilayers on 3C-SiC/Si(001)

Abstract

<jats:title>Abstract</jats:title> <jats:p>The suitability of Al<jats:italic> <jats:sub>x</jats:sub> </jats:italic>Ga<jats:sub>1−<jats:italic>x</jats:italic> </jats:sub>N nucleation layers (NLs) with varying Al fraction <jats:italic>x</jats:italic> for the metal organic vapour phase epitaxy of zincblende GaN on (001) 3C-SiC was investigated, using x-ray photoelectron spectroscopy, atomic force microscopy, and x-ray diffraction. The as-grown NLs exhibited elongated island structures on their surface, which reduce laterally into smaller, more equiaxed islands with increasing AlN composition. During high-temperature annealing in a mixture of NH<jats:sub>3</jats:sub> and H<jats:sub>2</jats:sub> the nucleation islands with low Al fraction ripened and increased in size, whereas this effect was less pronounced in samples with higher Al fraction. The compressive biaxial in-plane strain of the NLs increases with increasing AlN composition up to <jats:italic>x</jats:italic> = 0.29. GaN epilayers grown over NLs that have low Al fraction have high cubic zincblende phase purity and are slightly compressively strained relative to 3C-SiC. However, those samples with a measured Al fraction in the NL higher than 0.29 were predominantly of the hexagonal wurtzite phase, due to formation of wurtzite inclusions on various {111} facets of zb-GaN, thus indicating the optimal Al composition for phase-pure zb-GaN epilayer growth.</jats:p>