The effect of the carrier gas (H, N) upon the morphologies and defect characteristics of samples, which had been grown by epitaxial lateral overgrowth using hydride vapor-phase epitaxy, was studied. The growth was carried out on metalorganic vapor-phase epitaxial GaN which had been prepared on sapphire patterned with SiO2 stripes aligned along the <1¯1•0> GaN direction. The cross-sections of the epitaxial lateral overgrowth-grown stripes changed from trapezoidal to triangular, with increasing H content of 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, in stripes with a trapezoidal morphology, dislocations from the window region reached the sample

surface. In the case of triangular stripes, they were bent in the horizontal direction; away from the top surface. Cross-sectional cathodoluminescence microscopy revealed 2 distinct regions of luminescence intensity and nature. One of them exhibited near-bandgap excitonic emissions. The other exhibited a high-intensity blue-shifted emission band which was attributed to plasma recombination; thus indicating a high local free-carrier concentration due to intrinsic defects or impurities. These 2 regions were correlated with various growth facets rather than with the dislocation distribution. A 2-step growth method was developed which exploited the dependence of the morphology upon the gas composition. In the first step, the formation of triangular facets was encouraged. This bent any dislocations, which had propagated vertically from the seed layer, into the horizontal direction. In the second step, the layers were flattened by using conditions which favored lateral growth. Excellent control of faceting, and reproducibility of the selectively grown structures and layers, could be achieved. By means of spatially-resolved cathodoluminescence measurements, carried out on cleaved cross-sections of the layers, various domains could be identified and correlated with the growth mode. The epitaxial lateral overgrowth layers which were obtained by 2-step growth had significantly reduced dislocation densities (2 x 107 to 3 x 107/cm2) at the surface. The full-width at half-maximum of the X-ray rocking curve gave values which were 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.Gradečak, P.Stadelmann, T.Riemann, J.Christen: Journal of Applied Physics, 2002, 92[3], 1307-16