Spatial variation of optical and structural properties of ELO GaN directly grown on patterned sapphire by HVPE

Abstract

A 275 µm thick GaN layer was directly grown on the SiO2-prepatterned sapphire in a home-built vertical hydride vapour phase epitaxy (HVPE) reactor. The variation of optical and structure characteristics were microscopically identified using spatially resolved cathodeluminescence and micro-Raman spectroscopy in a cross section of the thick film. The D 0 XA line with the FWHM of 5.1 meV and etch-pit density of 9 × 106 cm−2 illustrated high crystalline quality of the thick GaN epitaxial layer. Optically active regions appeared above the SiO2 masks and disappeared abruptly due to the tapered inversion domains at 210–230 µm thickness. The crystalline quality was improved by increasing the thickness of the GaN/sapphire interface, but the region with a distance of 2 µm from the top surface revealed relatively low quality due to degenerate surface reconstruction by residual gas reaction. The x-ray rocking curve for the symmetric (0 0 2) and asymmetric (1 0 2) reflections also showed good quality and a small wing tilt of the epitaxial lateral overgrowth (ELO) GaN.