The driving force for dislocation multiplication in the substrate of misfitting heteroepitaxial systems

It is shown by a transmission electron microscopy investigation of the initial stages of growth of Si0.97Ge0.03 on Si(001) from In solution that dislocation multiplication in the substrate of these layers is related to the undulated surface morphology consisting of ridges and troughs (“crosshatch pattern”): dislocations are injected into the substrate but below the troughs of the crosshatch pattern only. Three-dimensional finite-element calculations of the shear stress distribution show that maximum shear stresses occur at trough sites, which results in preferential dislocation nucleation. The shear stresses in the substrate underneath the ridges of the undulated layers push these dislocation into the substrate and drive a Frank-Read multiplication source. The occurrence of shear stresses in the substrate due to an undulated surface morphology can be used to explain multiplication processes in the substrate observed by other authors. The model is thus generally valid.