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

摘要

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) × 10~(11) cm~(-2) and (1.1±0.9) × 10~6cm~(-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 (0001) wing of the ELOG sample, where the dislocation density was < 1 × 10~6 cm~(-2) and BSF density was (2.0 ± 0.7) × 10~4 cm~(-1). Of the in-situ techniques, SiN_x interlayers were most effective: the interlayer with the highest surface coverage that was studied reduced the BSF density to (4.0 ± 0.2) × 10~5cm~(-1) and the dislocation density was lowered by over two orders of magnitude to (3.5 ± 0.2) × 10~8cm~(-2).