Structural transformations produced in strain‐relaxed, low‐dislocation‐density Si0.6Ge0.4films by As+implantation and rapid thermal annealing were studied by transmission electron microscopy and x‐ray microanalysis. The type of residual defects was found to be strongly dependent on annealing temperature. Only perfect dislocation loops were observed in implanted layers after annealing at 800 °C. Annealing at higher temperature (900 °C) results in complete removal of irradiation damage accompanied by the formation of GeAs precipitates of monoclinic phase and spherical shape. The results show that the behavior of As in Si–Ge alloys during thermal processing is remarkably different from that in Si. In particular, precipitation of As atoms in Si0.6Ge0.4was found at an As concentration of 9×1020cm−3which is at least one order of magnitude lower than the critical As concentration for As precipitation in Si. ©1996 American Institute of Physics.