Synchrotron white beam X-ray topography and atomic force microscopy studies of a 540R-SiC Lely platelet

Optical Microscopy and Atomic Force Microscopy (AFM) of a SiC Lely platelet revealed a macrostep pattern the periodicity of which led to speculation that it possessed a structure with a repeat distance roughly 350 times the SiC bilayer thickness. Transmission Laue patterns recorded from the crystal revealed a 3-fold symmetric pattern, qualitatively similar to that obtained from the 6H structure, but displaying an immense number of closely-spaced reflections. The diffraction spots were resolved with a specimen-film distance of 1.4 m. The spacing of the spots in the 101̄/row indicated that the specimen's polytype was 540R. Synchrotron White Beam X-ray Topography (SWBXT) revealed the presence of growth dislocations emanating towards the platelet's growth facets, deformation-induced basal plane dislocations, and a group of superscrew dislocations close to the crystal's nucleation point. Optical microscopy revealed micropipes, which correlated with the superscrew dislocation images revealed by SWBXT. Preliminary calculations indicate that the total of the Burgers vectors of the observed micropipes was between 100 and 200 nm. Trails of basal plane dislocation etch pits were shown by Nomarski microscopy to intersect the etched crystal surface in a roughly periodic fashion. The trails were attributed to enhanced etching of the intersection across a 1° surface tilt of a series of basal plane dislocations distributed along the crystallographic c-axis with a periodicity related to that of the crystal surface's stepped ledges. This was confirmed using AFM, which revealed a faster etch rate at the intersections of basal plane dislocations at the ledges.