There was some question as whether micropipes in SiC crystals, giant dislocations that possessed hollow cores and lay roughly along the hexagonal c -direction, were screw dislocations with Burgers vectors of nc, where n was an integer, or were dislocations of mixed character, with Burgers vector nc+ma, where m was equal to n or possibly different from n. X-ray topographs of the basal faces of PVT-grown 4H-SiC wafers containing micropipes taken in both back-reflection and grazing-incidence geometries were compared with computer simulations of micropipe images. The deviation from circular symmetry of micropipe images in such topographs may be explained as well by the micropipe tilt from the c-direction as by an nc+ma nature. The contrast of micropipes in electron micrographs comprises of a pair of light and dark lobes consisting of a detailed system of subsidiary fringes. These were comparable with micropipe image computer simulations for Burgers vector nc. When an na edge component was introduced to the simulation, a small feature, a few hundred nm wide, appeared, which was absent from the micrographs.

The Character of Micropipes in Silicon Carbide Crystals. W.M.Vetter, M.Dudley: Philosophical Magazine, 2006, 86[9], 1209-25