The nucleation and microstructure of large-scale columnar domains present in hydride vapor phase epitaxial GaN layers grown directly on sapphire were studied by using cathodoluminescence and transmission electron microscopy. The domains were distributed in a quasi-continuous layer close to the GaN/sapphire interface. The domain boundaries were found to be associated with stacking mismatch defects. They were initiated at steps on the sapphire surface and were formed between nucleation islands growing on adjacent terraces. The formation of these domains in the initial stages of hydride vapor phase epitaxial GaN hetero-epitaxial growth was proposed 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