MBE-grown Si/Si1-xGe(x) heterostructures on (100) Si have been characterized by Rutherford backscattering spectroscopy (RBS), ion channeling and X-ray diffraction to investigate defect densities and tetragonal lattice distortion. Critical layer thickness and relaxation of strain by formation of misfit dislocations are strongly dependent on the growth temperature. A Si0.67Ge0.33 layer with a thickness of 2000 angstrom is found to be still fully strained at a growth temperature of 450-degrees-C, whereas the same layer grown at 550-degrees-C shows considerable strain relaxation by dislocations. To obtain better depth resolution than with conventional RBS, medium energy ion scattering (MEIS) experiments have been performed on Si/Ge superlattices with layer thickness of 10-40 angstrom. A position-sensitive toroidal electrostatic analyser was employed to detect the backscattered ions simultaneously over an angular range of 30-degrees with an energy resolution of 1 keV FWHM for 250 keV He ions, corresponding to a depth resolution of about 10 angstrom.