Surface pits in the form of V-shaped defects were investigated by the atomic force microscopy of films grown at 780C by metal-organic vapor phase epitaxy onto conventionally and pendeo-epitaxially deposited GaN thin film templates. The density of the V-shaped defects was similar to the density of threading dislocations (3 x 109/cm2) that originated from the hetero-epitaxial interface between the GaN template layer and the SiC substrate. The V-defect density decreased with decreasing dislocation density, following increased in the template layer thickness or the use of pendeo-epitaxial seed layers. A concomitant reduction in the full-widths at half-maximum of the X-ray rocking curves was also observed. A qualitative model was presented which described the formation of V-shaped defects as being the result of interactions between the movement of surface steps, screw-type dislocation cores and clusters of atoms on the terraces that formed under conditions of high surface undercooling.

Helical-Type Surface Defects in GaN Thin Films Epitaxially Grown on GaN Templates at Reduced Temperatures. P.Q.Miraglia, E.A.Preble, A.M.Roskowski, S.Einfeldt, R.F.Davis: Journal of Crystal Growth, 2003, 253[1-4], 16-25