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

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