Multiplication of misfit dislocations in In_xGa_1−xAs/GaAs heterostructures

Abstract

The misfit dislocation multiplication process which was observed for the first time in In_xGa_1−xAs/GaAs strained-layer superlattices (with x < 0·20) (A. Lefebvre, C. Herbeaux, C. Bouillet and J. Di Persio, 1991, Phil. Mag. Lett., 63, 23) is re-examined in detail in strained-layer superlattices and in metamorphic structures. Transmission electron microscopy reveals that this process is based on the occurrence of interactions between perpendicular 60° misfit dislocations with identical Burgers vectors and the subsequent glide of V inclined tips into the substrate, not much different from another multiplication process proposed in the Ge_xSi_1−x/Si system (F. K. LeGoues, B. S. Meyerson, J. F. Morar and P. D. Kirchner, 1992, J. appl. Phys., 71, 4230). The dissimilarity between the two processes is essentially due to differences in the mobilities of the dislocation segments constituting these inclined tips. In the Ge_xSi_1−x/Si system, a symmetrical glide of V inclined tips is observed whereas an asymmetrical glide is observed in the In_xGa_1−xAs/GaAs system. This asymmetric glide is caused the α part of the V inclined tip being much more mobile than the β part, which results in the formation of a screw segment-linked to this α part-which can then cross-slip in the {111} plane containing the β part. The last stage of the process involves the operation of Frank–Read sources that emit glissile dislocations into the {111} planes: parts of the half-loops which develop towards the epilayer are parallel to the interface and are then new β misfit dislocations.