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 °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. At 700 °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 °C, the SiGe is relaxed by misfit dislocations due to the increased density of born-in point defects at low temperatures.