Synchrotron white-beam X-ray topography, post-oxidation color mapping, atomic force microscopy and scanning electron microscopy were used to study the defect and polytype distribution in a thin film grown on mesas structures on part of a 4H-SiC crystal subjected to a non-optimum version of a reported procedure for achieving atomic flatness. This combination of techniques was used to confirm that atomic flatness could be achieved only on mesas which contained no screw dislocations. It was also found that most atomically flat mesas were of small size, as expected, since the probability of a screw dislocation threading a mesa was proportional to its area. For these small mesas, either no 3C-SiC nucleation, or complete coverage by one or another of the 3C variants, was observed. In mesas which contained screw dislocations (mostly those of larger size), either no 3C nucleation, or partial coverage by single or double phase 3C, was observed. In contrast to previous observations of on-axis mesa samples grown under various conditions for which polytypes such as 15R were observed, no polytypes other than 4H, 3C(I) and 3C(II) were detected anywhere on the wafer. In the absence of the stacking-sequence template which was provided by the risers of steps (due either to a screw dislocation or to the off-cut angle), this data indicated that no other polytype but 3C formed under these growth conditions. The study indicated that the combined use of synchrotron white-beam X-ray topography in back-reflection and forward-reflection geometry, post-oxidation color mapping, atomic force microscopy and scanning electron microscopy was ideally suited for the detailed microstructural and structural mapping of SiC.

Polytype Identification in Heteroepitaxial 3C-SiC Grown on 4H-SiC Mesas using Synchrotron White Beam X-ray Topography. M.Dudley, W.M.Vetter, P.G.Neudeck: Journal of Crystal Growth, 2002, 240[1-2], 22-33