Using photoluminescence we have studied the effect of a low temperature ‘‘preanneal’’ stage on the intermixing of 3 nm Si0.7Ge0.3/Si quantum wells, implanted with silicon ions having energies up to 1 MeV and then exposed to rapid thermal annealing at 850 °C for 300 s. We find that an unwanted quantum well band gap increase in unimplanted samples after rapid thermal annealing can be reduced substantially from ∼30 to ∼5 meV due to the removal of grown‐in defects by preannealing at 630 °C for 24 h. Preannealed samples that were implanted and rapid thermal annealed showed at least the same band gap increase (up to 70 meV in these samples) observed for nonpreannealed samples. These results are understood in terms of significantly different activation energies for defect diffusion and quantum well intermixing and a nonlinear dependence of the energy shifts on defect concentrations. ©1996 American Institute of Physics.