Atomic force microscopy was used to study the (00•1) growth surface of a 6H-type single crystal at points where micro-pipes emerged at the growth surface. All of the micro-pipes examined were at the origin of spiral steps; thus indicating that dislocations intersected the surface at these points. The dislocations which were observed at surface/micro-pipe intersections had Burgers vectors of at least 4b, where b was the Burgers vector of a unit screw dislocation which was aligned along the c-axis (b = 1.519nm). Single and double unit dislocations were also observed, but they were not associated with micro-pipes. Micron-sized deposits of heterogeneous phase were observed in the vicinity of the micro-pipes. The curvature of growth steps around these heterogeneities indicated that they impeded step motion when the crystal was growing. On the basis of the observations, a model was proposed for the formation of super-dislocation/micro-pipe complexes that involved the coalescence of unit screw dislocations which were forced towards one another as large steps grew around heterogeneous surface material.

J.Giocondi, G.S.Rohrer, M.Skowronski, V.Balakrishna, G.Augustine, H.M.Hobgood, R.H.Hopkins: Journal of Crystal Growth, 1997, 181, 351-62