High-energy (1 MeV), ion irradiation of GeSi/Si strained layers at elevated temperatures can cause strain relaxation. This study examines the defects responsible for relaxation and for the evolution of the strain during subsequent annealing. Three distinct annealing stages are identified and correlated with the defect microstructure. In the temperature range from 350 to 600 °C, a gradual recovery of strain is observed. This is shown to correlate with annealing of small defect clusters and the growth of voids. The voids are visible at annealing temperatures in excess of 600 °C, consistent with an excess vacancy concentration in the irradiated alloy layer. In the temperature range 600–750 °C, the strain recovers to a maximum value which is correlated with the ripening of voids, dissolution of alloy layer {113} rodlike defects, and {113} planar interstitial defects in the substrate. At temperatures in the range 750–1000 °C, strain relaxation is observed and is correlated with the growth of intrinsic dislocations within the alloy layer. These intrinsic, looplike dislocations nucleate at the alloy–substrate interface and grow within the alloy layer, toward the surface. ©1998 American Institute of Physics.