An assessment was made of the relative effectiveness of techniques for reducing the defect density in hetero-epitaxial non-polar a-plane GaN films grown onto r-plane sapphire by metalorganic vapour phase epitaxy. The defect reduction techniques studied were: 3D–2D growth, SiNx interlayers, ScN interlayers and epitaxial lateral overgrowth (ELOG). Plan-view transmission electron microscopy showed that the GaN layer grown in a 2D fashion had a dislocation and basal-plane stacking fault (BSF) density of 1.9 x 1011/cm2 and 1.1 x 106/cm, 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 (00•1) wing of the ELOG sample, where the dislocation density was <106/cm2 and BSF density was 2.0 x 104/cm. 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 x 105/cm and the dislocation density was lowered by over two orders of magnitude to 3.5 x 108/cm2.

Assessment of Defect Reduction Methods for Nonpolar a-Plane GaN Grown on r-Plane Sapphire. C.F.Johnston, M.J.Kappers, M.A.Moram, J.L.Hollander, C.J.Humphreys: Journal of Crystal Growth, 2009, 311[12], 3295-9