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, SiNx 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)×1011 cm−2 and (1.1±0.9)×106 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 <1×106 cm−2 and BSF density was (2.0±0.7)×104 cm−1. Of the in-situ techniques, SiNx interlayers were most effective: the interlayer with the highest surface coverage that was studied reduced the BSF density to (4.0±0.2)×105 cm−1 and the dislocation density was lowered by over two orders of magnitude to (3.5±0.2)×108 cm−2.