Investigations of the origins of surface roughening in GaN(00•1) resulted in the development of a growth process which used an optimum temperature of 1020C and a film thickness of above 2.5μm to yield films having the smoothest surface morphology. Atomic force microscopy revealed uncoalesced GaN islands and hillocks when using temperatures below and above the optimum of 1020C, respectively. Uncoalesced islands were the result of insufficient lateral growth. Hillocks were the result of rotation of heterogeneous steps which formed at pure screw or mixed dislocations that terminated on the (00•1) surface. Growth of the latter features was controlled kinetically by the temperature, via adatom diffusion. The 106/cm2 density of hillocks was reduced by growth on thick GaN templates and regions of pendeo-epitaxy overgrowth with lower pure screw or mixed dislocation contents. Smooth pendeo-epitaxial surfaces were obtained at temperatures that reduced the lateral to vertical growth rate ratio but also retarded hillock growth that originated in the stripe regions. The (11•0) pendeo-epitaxy side-wall surface was atomically smooth, with a root-mean-square roughness of 0.17nm (noise-limited resolution of atomic force microscopy).

Surface Instability and Associated Roughness during Conventional and Pendeo-Epitaxial Growth of GaN(0001) Films via MOVPE. A.M.Roskowski, P.Q.Miraglia, E.A.Preble, S.Einfeldt, R.F.Davis: Journal of Crystal Growth, 2002, 241[1-2], 141-50