Threading dislocations in thin (<200nm) AlN nucleation layers grown by metal-organic chemical vapor deposition on top of 4H-SiC on-axis mesas with atomic-scale steps were analyzed by transmission electron microscopy. The AlN nucleation layer controlled threading dislocations in an overlying ~2µm GaN layer through 2 identified mechanisms: threading half-loop formation and dislocation bending at V-shaped pits. Threading dislocations in the AlN film could be traced directly to bilayer 4H-SiC steps at the substrate/film interface. These observations reveal several approaches to extended defect reduction in GaN films grown on 4H-SiC.

Threading Dislocation Behavior in AlN Nucleation Layers for GaN Growth on 4H-SiC. Y.N.Picard, M.E.Twigg, M.A.Mastro, C.R.Eddy, R.L.Henry, R.T.Holm, P.G.Neudeck, A.J.Trunek, J.A.Powell: Applied Physics Letters, 2007, 91[1], 014101 (3pp)