Mechanism of Heteroepitaxy of GaN Grown on Sapphire Substrate(<Special Issue>Mechanism of Heteroepitaxy)

Abstract

The role of an AlN buffer layer used to obtain uniform and high-quality GaN in the heteroepitaxial growth by MOVPE on sapphire (α-Al_2O_3) substrates has been studied. The initial growth processes of GaN grown with and without the A1N buffer layer shown by SEM images, and the GaN/AlN/sapphire interface is observed by cross sectional TEM images. The crystalline structure of GaN near the AlN interface reveals that the geometric selection of columnar GaN crystals causes the arrangement of the crystalline direction which results in the improvement of the crystalline quality. In the case without the AlN buffer layer, three dimensional island growth occurs; but in the case with the AlN buffer layer, three dimensional growth is converted to two dimensional growth, I. E. layer-by-layer growth after the smooth coalescence of the islands.