Self-ordering of misfit dislocation segments in epitaxial SiGe islands on Si(001)

Ordering of misfit dislocation segments in concentric polygons at the base of SiGe epitaxial islands on Si(001) has been recently indicated by in situ Transmission Electron Microscope observation. In this paper we confirm the very regular spacing by Atomic Force Microscope and He-ion Microscope measurements of the footprint carved in the Si substrate by the plastic events. We explain the intriguing ordering, as obtained with no gliding rearrangements, by cyclic occurrence of the thermodynamic critical conditions for plastic events. Quantitative predictions by a fully analytical model, which includes the dependence on island shape and composition in the generation of misfit dislocations, matched very well experimental measurements.