The influence of sapphire substrate orientation on crystalline quality of GaN films grown by hydride vapor phase epitaxy

GaN films were grown by hydride vapor phase epitaxy on sapphire substrates with orientations c-(0 0 0 1), a-(1 1 2-bar 0), m-(1 0 1-bar 0) and r-(1 0 1-bar 2) using N2 as a carrier gas. The crystalline perfection of the grown films was studied by X-ray diffraction, by optical microscopy and scanning electron microscopy and by microcathodoluminescence (MCL). It was found that, for c- and a-oriented sapphire substrates, the GaN films showed (0 0 0 1) orientation, for m-oriented sapphire the films showed semi-polar (1 0 1-bar 3) orientation, while for r-sapphire substrates GaN layers with non-polar a(1 1 2-bar 0) orientation could be grown. The surface morphology of the GaN films and their crystalline structure strongly depended on the substrate orientation. With increasing the layer thickness the halfwidth of the X-ray rocking curves monotonically decreased which points to improvement of the crystalline quality. The best quality films were grown for the c- and r-oriented substrates: respectively, 460 arcseconds at the thickness of 400 mm, 600 arcseconds at the thickness of 300 μm. For m-oriented substrates the halfwidth was 1300 arcseconds at comparable thickness. The density of stacking faults for semi-polar and non-polar films was determined by MCL imaging. The linear density of stacking faults was found to be 5x104 cm-1 for films grown on m-oriented sapphire substrates and 5103 cm-1 for a-GaN films grown on r-sapphire.