MBE-grown, relaxed epitaxial Si1-xGex alloy layers with x=0.4 and 0.5 were studied by transmission electron microscopy (TEM), photoluminescence, atomic force microscopy (AFM) and channeling. The TEM studies did not reveal any extended defects in the layers, except for threading dislocations of a density less than or equal to 10(6) cm(-2). Strong near-band luminescence due to bound excitons indicates a high quality of the films. Preferential chemical etching combined with AFM allowed us to detect the density of threading dislocations, which was estimated to be similar to 10(6) cm(-2) for x = 0.4 and 0.5. A deviation from perfect crystallinity was observed by channeling. The channeling parameters were measured as a function of depth by removal of thin layers by polishing; no depth dependence of the channeling parameters was detected.