Heterostructures of Si1-xGex/Si with Ge content x from 14 to 67%, grown on Si by atmospheric pressure chemical vapor deposition (APCVD) at 650 or 700 degrees C, have been studied by photoluminescence (PL) spectroscopy, Normarski microscopy after Schimmel etching, atomic force microscopy (AFM) and secondary ion mass spectroscopy (SIMS). For SiGe grown by APCVD with a low Ge content (<40%), strain relaxation is achieved by misfit dislocation formation. For high Ge content (>40%), the relaxation mode is influenced by the deposition temperature, where the energetically most favorable mechanism will dominate. Al 700 degrees C, the SiGe is relaxed by 3D island formation and the PL alloy band can be correlated to island structuring of the surface. At 650 degrees C, the SiGe is relaxed by misfit dislocations due to the increased density of born-in point defects at low temperatures.