MULTIPLICATION OF MISFIT DISLOCATIONS IN INXGA1-XAS/GAAS HETEROSTRUCTURES

The misfit dislocation multiplication process which was observed for the first time in In(x)Ga1-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-degrees 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(x)Si1-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(x)Si1-x/Si system, a symmetrical glide of V inclined tips is observed whereas an asymmetrical glide is observed in the In(x)Ga1-xAs/GaAs system. This asymmetric glide is caused by the alpha part of the V inclined tip being much more mobile than the beta part, which results in the formation of a screw segment-linked to this alpha part - which can then cross-slip in the {111} plane containing the beta 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 beta misfit dislocations.