AN ATOMIC-FORCE MICROSCOPY STUDY OF SUPER-DISLOCATION MICROPIPE COMPLEXES ON THE 6H-SIC(0001) GROWTH SURFACE/

We have used atomic force microscopy (AFM) to study the (0 0 0 I) grow th surface of a 6H-SiC single crystal at the points where micropipes e merge on the growth surface. All of the micropipes examined are origin s of spiral steps, indicating that dislocations intersect the surface at these points. The dislocations observed at the surface/micropipe in tersections have Burgers vectors of at least 4b(0), where b(0) is the Burgers vector of a unit screw dislocation aligned along the c-axis (b (0) = 15.19 Angstrom). Single and double unit dislocations were also o bserved, but they are not associated with micropipes. Micron-scale dep osits of a heterogeneous phase were observed in the vicinity of the mi cropipes. The curvature of growth steps around these heterogeneities i ndicates that they impeded step motion while the crystal was growing. Based on our observations, we propose a model for the formation of sup er-dislocation/micropipe complexes that involves the coalescence of un it screw dislocations that are forced towards one another as large ste ps grow around heterogeneous material on the surface.