ATOMISTIC STUDY OF DISLOCATION NUCLEATION IN GE/(001)SI HETEROSTRUCTURES

Nucleation of misfit dislocations in Ge/(001)Si heterostructures is investigated theoretically by an atomistic model based on the Stillinger-Weber potential (Stillinger and Weber 1985, Phys. Rev. B, 31, 5262). Both 60 degrees and 90 degrees dislocations are considered, and the energy is calculated as a function of distance of dislocations from the free surface in a thin-film heterostructure. The critical thicknesses of the dislocation nucleation obtained from the atomistic simulation are larger than the previously reported results of the continuum analysis, and we attribute this difference mainly to core energy of dislocations. The activation barrier for dislocation nucleation from the surface is estimated from the variation of energy with distance of a dislocation from the surface. The calculated activation energy is much larger than the thermal energy at normal growth temperatures. We also discuss the interaction between two 60 degrees dislocations and the formation of a 90 degrees dislocation at the interface by a dislocation reaction mechanism.