The nucleation and microstructure of large-scale columnar domains in hydride vapor-phase epitaxial GaN layers, grown directly onto sapphire, were studied by using cathodoluminescence and transmission electron microscopy. The domains were distributed within a quasi-continuous layer close to the GaN/sapphire interface. The domain boundaries were found to be associated with stacking mismatch defects. They

initiated at steps on the sapphire surface and formed between nucleation islands growing on adjacent terraces. The formation of these domains in the initial stages of hydride vapor-phase epitaxial hetero-epitaxial growth was suggested to play an important role in the strain-relaxation mechanism.

Misfit Defect Formation in Thick GaN Layers Grown on Sapphire by Hydride Vapor Phase Epitaxy. E.Valcheva, T.Paskova, P.O.Å.Persson, L.Hultman, B.Monemar: Applied Physics Letters, 2002, 80[9], 1550-2