Epitaxial lateral overgrowth of GaN on sapphire - An examination of epitaxy quality using synchrotron X-ray topography

Section transmission white beam X-ray topography was applied to the evaluat ion of the growth of GaN on sapphire using the epitaxial lateral overgrowth (ELO) technique. Using openings in 100 nm thick SiO2 windows, a new GaN gr owth took place, which resulted in nominal overgrowth thicknesses of 6.8 mu m Measurements of the recorded Laue section topographs revealed misorientat ion between the epilayer and the substrate. Neglecting the misorientation c ontribution due to the 30 degrees rotation of the epilayer with respect to the substrate, the misorientation mechanism was found to be a consequence o f lattice relation and dilatation. In the case of the ELO sample, these par ameters varied with the stripe/window dimensions. The quality of the ELO ep ilayer is improved when compared to the non-ELO sample, though some local d eviations from lattice coherence were observed. These results were compleme nted by observations made using X-rap diffraction and transmission electron microscopy.