The influence of the carrier gas (H or N) upon the morphology and defect characteristics of GaN grown by using the epitaxial lateral overgrowth method was studied by using hydride vapor phase epitaxy. Growth was carried out on metal-organic vapor phase epitaxy GaN/sapphire patterned with SiO2 stripes, aligned along the <1¯1•0> GaN direction. The cross-sections of the epitaxial lateral overgrown stripes changed from trapezoidal to triangular, with increasing H content in the carrier gas, due to a change in the ratio of the growth velocities on the {11•2} and (00•1) facets. Transmission electron microscopic observations showed that, while in stripes with a trapezoidal morphology, dislocations from the window region still reached the sample surface. For triangular stripes, they were bent in the horizontal direction; away from the top surface. Cross-sectional cathodoluminescence microscopy revealed 2 basically distinct regions of luminescence intensity. One exhibited near-bandgap excitonic emissions. The other exhibited a high-intensity blue-shifted emission band which was attributed to e–h plasma recombination; indicating a high local free carrier concentration due to intrinsic defects or impurities. These 2 regions were related to differing growth facets, and not to the dislocation distribution. An original 2-step growth method was developed which exploited the dependence of the morphology upon the gas phase composition. In the first step, the formation of triangular facets was preferred. This was done in order to bend dislocations, which had propagated vertically from the seed layer, into the horizontal direction. In the second step, the layers were planarized by using conditions which favored lateral growth. Very good control of the faceting, and a high reproducibility of the selectively grown structures and layers, could be obtained. The epitaxial lateral overgrowth layers, obtained by 2-step growth, had significantly reduced dislocation densities (2 x 107 to 3 x 107/cm2) at the surface. This was comparable with the best published values of hydride vapor-phase epitaxial lateral overgrowth. The full-width at half-maximum of the X-ray rocking curve gave values of below 200arcsec.

Influence of the Carrier Gas Composition on Morphology, Dislocations and Microscopic Luminescence Properties of Selectively Grown GaN by Hydride Vapor Phase Epitaxy. V.Wagner, O.Parillaud, H.J.Bühlmann, M.Ilegems, S.Gradecak, P.Stadelmann, T.Riemann, J.Christen: Journal of Applied Physics, 2002, 92[3], 1307-16