A low dislocation density (107 to 108/cm2) was obtained in thin GaN films, on 6H-type (00•1) SiC substrates, which had been grown by means of metalorganic chemical vapor deposition. Two major requirements were identified for the reduction of dislocation densities. These were the use of ultra-thin AlN buffer layers and smooth AlN surfaces at the atomic scale. The effects of the surface roughness and structural perfection of the AlN buffer layer upon GaN film quality were extensively investigated as a function of the AlN film thickness. The reduced dislocation density was made possible by using AlN buffer layers with a thickness of about 1.5nm. The latter was below the critical value for misfit dislocation generation. The smoother surface morphology and enhanced structural quality of ultra-thin AlN buffer layers were found to be the main factors which reduced the defect density in the GaN film.

S.Tanaka, S.Iwai, Y.Aoyagi: Journal of Crystal Growth, 1997, 170, 329-34