Defect structures in GaN films grown onto a convex patterned sapphire substrate were investigated, in order to determine the origin of structural improvement, by means of transmission electron microscopy and laser confocal scanning microscopy. From the transmission electron microscopy results, it was deduced that most of the threading dislocations in the trench region of the convex patterned sapphire substrate were bent by a lateral growth mode. Also staircase-like threading dislocations were observed near the curved slant region of the convex pattern; they converged at the top of the convex patterned region by staircase-upward propagation. This scenario seemed effectively to prevent threading dislocations from vertical propagation in the trench region. The photoluminescence mapping and spectra obtained by laser confocal scanning microscopy were consistent with these results from transmission electron microscopy observations. The generation of staircase-like threading dislocations was related to the formation of a terraced surface during growth, and suggested a probable mechanism that changed the propagation direction of threading dislocations via the curved surface of the convex patterned sapphire substrate. The lateral growth and staircase-upward propagation of threading dislocations were major factors in the structural improvement of GaN film grown onto convex patterned sapphire substrates.

Defect Structure Originating from Threading Dislocations Within the GaN Film Grown on a Convex Patterned Sapphire Substrate. T.S.Oh, H.Jeong, Y.S.Lee, T.H.Seo, A.H.Park, H.Kim, K.J.Lee, M.S.Jeong, E.K.Suh: Thin Solid Films, 2011, 519[8], 2398-401