Transmission electron microscopy characterisation of metalorganic chemical vapour deposition grown GaN layers

GaN layers grown onto sapphire substrates by metalorganic chemical vapour deposition were characterised by optical microscopy, transmission electron microscopy and atomic force microscopy measurements. Mirror like surfaces were obtained at certain growth conditions despite the hexagonal based pyramids found on the growth surface. The typical pyramids have a base diameter of 20-30 mu m and height of about 1.5-3 mu m. The GaN layers are of the wurtzite type and epitaxially oriented to the sapphire substrate. Beside the threading dislocations, hexagonal rods of GaN surrounded by inversion domain boundaries are observed. An AlN layer has been formed at the interface region during the nitridation process of sapphire. (C) 1997 Elsevier Science S.A.