Dislocation Evolution and Microstructural Properties on GaN Grown on Cone Patterned Sapphire Substrate

Abstract

GaN epifilms are grown on the cone patterned sapphire substrates (CPSS) and the conventional sapphire substrates (CSS) by metal-organic chemical vapor deposition (MOCVD) using a two-step growth. We investigated dislocation structures and density in the GaN epifilms grown on CPSS and CSS using high resolution X-ray diffraction (HRXRD) and transmission electron microscopy (TEM). HRXRD measurement shows that GaN epifilms grown on CPSS have lower dislocation density than the CSS, especially the edge dislocation density. This consequence is confirmed by metallographs of etched GaN. From the TEM results, we found that most of the threading dislocations (TDs) in the trench region of the CPSS were bent by lateral growth mode. The bending of dislocations and presence of voids dramatically prevent the generation of threading dislocations on the surface due to the induced lateral overgrowth mode. The high Raman peak intensity of the GaN epifilms grown on CPSS with a low full width at half maximum (FWHM) indicates that there is an improvement in the quality of the GaN compared to GaN epifilms grown on CSS.