Effects of AlN buffer on the physical properties of GaN films grown on 6H-SiC substrates

In this study, 1.5-μm-thick GaN films with AlN buffer were prepared on 6H-SiC substrates by metal-organic chemical vapor deposition. To determine the effects of growth conditions of AlN buffer on crystalline quality and stress state of GaN films, two series of experiments were carried out. By optimizing growth conditions of AlN buffer, the full width at half maximum values of (0002) and (101¯2)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(10\bar{1}2)$$\end{document} rocking curves of GaN films were improved to 136 and 225 arcsec, respectively. A smooth surface was obtained with a small root-mean-squared roughness of 0.332 nm and the excellent optical property was observed. Simultaneously, threading dislocation density and tensile stress in GaN films were reduced by increasing AlN buffer growth temperature and its thickness in some extent. Besides, stress values in GaN films were confirmed by Raman and low-temperature photoluminescence spectra, which indicated that the lower tensile stress in GaN film, the higher the film crystallinity.