Temperature dependence of molecular beam epitaxy of GaN on SiC (0001)

High quality gallium nitride thin films have been grown on 6H-silicon carbi de (0001) substrates at varying substrate temperatures using molecular beam epitaxy and characterized at low and high film thicknesses. The epitaxial layers show two regimes in temperature distinguishable by different morphol ogy. For film thicknesses around the critical thickness, low temperature-gr owth is two dimensional while for higher temperatures, growth is in the for m of three-dimensional columnar islands. At a thickness of about 200 nm, th e low temperature films show a large density of spiral growths while high t emperature films show a two-dimensional morphology. X-ray peak widths are s een to decrease with increasing substrate temperature. These results have b een explained in terms of a model which proposes different misfit dislocati on formation mechanisms in the two temperature regimes. (C) 1999 American V acuum Society. [S0734-2101(99)09804-8].