SiC crystals of high structural perfection were investigated with several methods of X-ray diffraction topography in Bragg-case geometry. The methods included section and projection synchrotron white beam topography and monochromatic beam topography. The investigated 6H and 4H samples contained in large regions dislocations of density not exceeding 10 3 cm -2 .Most of them cannot be interpreted as hollow core dislocations (micro-or nanopipes). The concentration of the latter was lower than 10 2 cm -2 . The present investigation confirmed the possibility of revealing dislocations with all used methods. The quality of presently obtained Bragg-case multi-crystal and section images of dislocation enabled analysis based on comparison with numerically simulated images. The analysis confirmed the domination of screw-type dislocations in the investigated crystals.

The numerical simulation has been applied for studying of Bragg-case section topographic images of dislocation and rod-like inclusions. The validity of simple approximation of extinction contrast was confirmed in the case of screw dislocations in silicon carbide crystals. A procedure for approximate calculation of the strain field of rod-like inclusion was constructed, consisting of adding the contributions from a very large number of point-like inclusions uniformly distributed inside the assumed volume of the inclusion. The procedure ensured a reasonable similarity between the simulated topographs and experimental Bragg-case section topographic images of some pipe-formed cavities in silicon carbide crystals. The method is useful for some other materials, e.g. it enabled to compute realistic simulation of plane-wave topographs of the rod-like inclusions in YAG.

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Undoped 4H silicon carbide epitaxial layers were deposited by means of CVD method with growth rates of 2 µm/h, 5 µm/h and 11 µm/h at 1540• and 0• o-cut 4H-SiC (00 · 1) substrates. The structural defects were studied before and after growth of the epitaxial layers by means of conventional Lang topography, synchrotron white beam and monochromatic beam topography and by means of X-ray specular reectometry. The topographic investigations conrmed the continuation of the dislocations in the epitaxial deposit on the 8• and 4• o-cut substrates without new extended defects. The important dierence occurred in the surface roughness of the epitaxial layers, which increased for higher growth rates. The epitaxial layers grown on 0• o-cut substrates at analogous condition contained usually other SiC polytypes, but the inuence of the growth rate on the distribution of the polytypes was observed.