Mechanisms of impurity incorporation during MOVPE growth of m-plane GaN layers on LiAlO2

Abstract

We study the oxygen incorporation during growth of m-plane GaN films on LiAlO2 substrates by metal organic vapour phase epitaxy (MOVPE). A broad peak at ~550 nm in photoluminescence spectra is probably caused by oxygen impurities. Secondary ion mass spectroscopy (SIMS) confirms this finding and reveals a concentration in the order of 1019 cm-3 which is consistent to the measured n-type doping level. A general slow decrease of the oxygen concentration in growth direction is observed. A c-plane GaN film grown on sapphire co-loaded together with a piece of LiAlO2 shows a slightly increased doping concentration compared to a c-plane GaN reference. However, the achieved concentration of ~1017 cm-3 is much lower compared to m-plane GaN films. Growth of GaN on a backside-coated GaN/LiAlO2 template does neither suppress the impurity incorporation. This implies that oxygen incorporation via the gas phase is not the dominant factor. The SIMS oxygen profile of this GaN film on the template shows a strong peak at the position of growth interruption indicating the formation of a surface oxide. We assume that the m-plane GaN surface has a large affinity for oxygen at the deposition temperature which leads to the high oxygen impurity level. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.