The dislocation structure at the initial stage of relaxation of GexSi1-x films (x similar to 0.4-0.8) grown on Si (0 0 1) substrates tilted at 6 to the nearest (1 1 1) plane is studied. The use of Si substrates tilted away from the exact (0 0 1) orientation for epitaxial growth of GexSi1-x films (x >= 0.4) allowed finding the basic mechanism of formation of edge dislocations that eliminate the mismatch stresses. Though the edge dislocations are defined as sessile dislocations, they are formed in accordance with the slipping mechanism proposed previously by Kvam et al. (1990). It is highly probable that a 60 degrees misfit dislocation (MD) propagating by the slipping mechanism provokes the nucleation of a complementary 60 degrees MD slipping in a mirror-like tilted plane (1 1 1). The reaction between these dislocations leads to the formation of an edge MD that ensures more effective reconciliation of the discrepancy. Comparative estimation of the slip velocities of the primary and induced 60 degrees MDs and also of the resultant 90 degrees MD is fulfilled. The slip velocity of the induced 60 degrees MD is appreciably greater than the velocity of the primary 60 degrees MD. Therefore, the induced MD "catches up" with the second front of the primary MD, thus forming a 90 degrees MD propagating to both sides due to slipping of the 60 degrees MDs forming it. The propagation velocity of the 90 degrees MD is also greater than the slip velocity of a single 60 degrees MD. For these reasons, 90 degrees MDs under certain conditions that favor their formation and propagation can become the main defects responsible for plastic relaxation of GeSi films close to Ge in terms of their composition. (C) 2010 Elsevier B.V. All rights reserved.