The dislocation structure of GexSi1−x films (x = 0.4 to 0.8) grown by molecular-beam epitaxy on Si(001) substrates was studied by means of transmission electron microscopy. It was found that the density of edge misfit dislocations formed at the early stage of plastic strain relaxation in the films could exceed the density of 60° misfit dislocations. In previous publications, a predominant mechanism underlying the early formation of edge misfit dislocations in GexSi1−x/Si films with x>0.4 was identified; this mechanism involved the following processes. A 60° glissile misfit dislocation provoked nucleation of a complementary 60° misfit dislocation gliding on a mirror-like tilted plane (111). A new edge misfit dislocation formed as a result of interaction of the two complementary 60° misfit dislocations, and the length of the newly formed edge misfit dislocation could then be increased following the motion of the “arms” of the complementary 60° misfit dislocations. Based upon this scenario for the edge misfit dislocation generation process, the critical thickness of insertion of an edge misfit dislocation into GeSi layers of different compositions was calculated using the force balance model. The obtained values were found to be more than twice as low as the similar values for 60° misfit dislocations. This result suggested that a promising strategy towards obtaining dislocation arrays dominated by 90° dislocations in MBE-grown GexSi1−x/Si films could be implemented through preliminary growth on the substrate of a thin, slightly relaxed buffer layer with 60° misfit dislocations present in this layer. The dislocated buffer layer, acting as a source of threading dislocations, promotes the strain relaxation in the main growing film through nucleation of edge misfit dislocations in the film/buffer interface. It was shown that in the presence of threading dislocations penetrating from the relaxed buffer into the film nucleation of edge misfit dislocations in the stressed film could be initiated even if the film thickness remained small in comparison with the critical thickness for insertion of 60° misfit dislocations. Examples of such unusual misfit dislocation generation processes were found in the literature.

Edge Misfit Dislocations in the GeSi/Si(001) Pair: Conditions and Specific Features of High-Quantity Generation. Y.B.Bolkhovityanov, A.S.Deryabin, A.K.Gutakovskii, L.V.Sokolov: Journal of Crystal Growth, 2012, 338[1], 12-5