Modeling the plastic relaxation onset in realistic SiGe islands on Si(001)

A detailed investigation of plastic relaxation onset in heteroepitaxial SiGe islands on Si (001) is presented. The strain field induced by a straight misfit-dislocation segment is modeled by finite-element-method (FEM) calculations in three dimensions, fully taking into account the interaction with the multifaceted free surfaces of realistic islands. The total elastic energies before and after the placement of a 60 S dislocation segment in the most favorable position are therefore evaluated by a full FEM approach, for different island sizes and compositions. The critical volumes with composition for inserting the dislocation are finally obtained and successfully compared with the data in a report by Marzegalli et al. [Phys. Rev. Lett. 99, 235505 (2007)], where experimental values are compared to a simpler approach.