Real-time transmission electron microscopic observations of the interactions between threading and misfit dislocations in SiGe heterostructures were used to investigate such interactions in a quantitative manner. In addition to the expected long-range blocking of threading segments, a new short-range mechanism was observed which was significantly more effective. Simulations showed that this reactive blocking occurred when 2 dislocations having the same Burgers vector were reconnected. The ranges of epilayer thickness and composition at which the motion of epilayer threading dislocations could be halted (by interaction with pre-existing interfacial segments during hetero-epitaxial growth and annealing) were delineated. It was found that these interactions could halt dislocation motion at strain levels that were substantially above the critical thickness. At the highest levels of strain, those dislocations which became blocked were those which had parallel Burgers vectors. Numerical simulations showed that, for these cases, the dislocations underwent reconnection at the interface that caused the blocking. This contrasted with the previously predicted blocking mechanism, which had required that dislocation-blocking be only the result of long-range elastic repulsion between dislocations. The present results indicated that dislocation blocking could limit the rate of hetero-epitaxial strain relaxation at epilayer thicknesses which exceeded those of present models.

New Mechanism for Dislocation Blocking in Strained Layer Epitaxial Growth E.A.Stach, K.W.Schwarz, R.Hull, F.M.Ross, R.M.Tromp: Physical Review Letters, 2000, 84[5], 947-50