Assessment of defect reduction methods for nonpolar a-plane GaN grown on r-plane sapphire

This work assesses the relative effectiveness of four techniques to reduce the defect density in heteroepitaxial nonpolar a-plane GaN films grown on r-plane sapphire by metalorganic vapour phase epitaxy (MOVPE). The defect reduction techniques studied were: 3D-2D growth, SiN(x) interlayers, ScN interlayers and epitaxial lateral overgrowth (ELOG). Plan-view transmission electron microscopy (TEM) showed that the GaN layer grown in a 2D fashion had a dislocation and basal-plane stacking fault (BSF) density of (1.9 +/- 0.2) x 10(11)cm(-2) and (1.1 +/- 0.9) x 10(6) cm(-1), respectively. The dislocation and BSF densities were reduced by all methods compared to this 2D-grown layer (used as a seed layer for the interlayer and ELOG methods). The greatest reduction was achieved in the (0 0 0 1) wing of the ELOG sample, where the dislocation density was < 1 x 10(6) cm(-2) and BSF density was (2.0 +/- 0.7) x 10(4) cm(-1). Of the in-situ techniques, SiN. interlayers were most effective: the interlayer with the highest surface coverage that was studied reduced the BSF density to (4.0 +/- 0.2) x 10(5) cm(-1) and the dislocation density was lowered by over two orders of magnitude to (3.5 +/- 0.2) x 10(8) cm(-2). (C) 2009 Elsevier B.V. All rights reserved.