The growth of five layers of InAs quantum dots embedded in GaAs matrices was investigated by in situ synchrotron X-ray diffraction. Time-resolved X-ray diffraction revealed the evolution of the strains and height of quantum dots during the entire growth process including the nucleation of islands and encapsulation with GaAs at various substrate temperatures. Comparisons of in situ X-ray results with postgrowth photoluminescence spectra showed a clear correlation between the structural and optical properties. (C) 2008 Elsevier B.V. All rights reserved.