Metal-organic chemical vapor-deposited GaN, on the N-polar surface of GaN substrates, was found to exhibit gross hexagonal pyramidal features which were some 10 to 50μm in size; depending upon the layer thickness. The evolution of the pyramidal defects was governed by the growth rate of an emergent core of inversion domain which was some 100nm in size. The inversion domains nucleated at a thin band of O-containing amorphous material which was 2 to 5nm thick. The latter was a remnant of the mechanochemical polishing technique which was used to prepare the substrates before growth. As well as pyramidal hillocks, flat-topped hillocks also formed. These features were associated with the core dislocations which were the source of growth steps. Improvements in the substrate-polishing procedure permitted the effective elimination of the surface hillocks.

Morphological and Structural Characteristics of Homoepitaxial GaN Grown by Metalorganic Chemical Vapour Deposition. J.L.Weyher, P.D.Brown, A.R.A.Zauner, S.Müller, C.B.Boothroyd, D.T.Foord, P.R.Hageman, C.J.Humphreys, P.K.Larsen, I.Grzegory, S.Porowski: Journal of Crystal Growth, 1999, 204[4], 419-28