Carrier Gas Dependence at Initial Processes fora-Plane AlN Growth onr-Plane Sapphire Substrates by Hydride Vapor Phase Epitaxy

Abstract

The influence of the carrier gas used during the thermal cleaning of r-plane sapphire substrates and the subsequent first AlN layer growth at 1050 °C on two-step growth of a-plane AlN layers by hydride vapor phase epitaxy (HVPE) was investigated. When hydrogen (H2) was used as the carrier gas, the decomposition of r-plane sapphire occurred during the thermal cleaning, and unintentional nitridation of the sapphire surface occurred at the beginning of the growth of the first AlN layer, which resulted in the occurrence of misoriented AlN grains in the second AlN layer grown at 1450 °C. When a mixture of H2 and nitrogen (N2) was used as the carrier gas, nitridation of the sapphire surface occurred during the thermal cleaning, which also resulted in the occurrence of misoriented AlN grains. A single-crystalline a-plane AlN layer free of misoriented grains could be obtained by using only N2 as the carrier gas during the thermal cleaning and the growth of the first AlN layer to prevent nitridation of the sapphire surface.