GexSi1-x/Si(001) heterostructures with constant composition of Ge (x = 0.19-0.32) are grown by low-temperature (300-400 degrees C) molecular-beam epitaxy. Transmission electron microscopy reveals dislocation half-loops in the subsurface region of the stressed film, which is associated with nucleation of dislocations on elements of the three-dimensional relief on the surface of the growing or annealed film. Dislocation-nucleation centers are reproductive and form families of closely located misfit dislocations of the same sign. The use of a hydrogen atmosphere for annealing the GeSi film yields a lower rate of generation of misfit dislocations than annealing in vacuum or argon.(c) 2006 Elsevier B.V. All rights reserved.