Stability of dislocations in epitaxially strained semiconductor stripe films

The energy change on introducing a misfit dislocation into an epitaxially strained semiconductor stripe of height h and width 2l has been estimated for dislocations parallel to the stripe direction (longitudinal) and across the stripe (transverse). The stress distribution in the stripe (in the absence of dislocations) was calculated using a finite element method, which gives much lower normal stresses than those predicted by an earlier analytical model. The reduced stresses result in correspondingly greater stability of the film with respect to introduction of a longitudinal dislocation. For example, the critical misfit strain for introduction of a longitudinal dislocation into a stripe with h/l = 1 is over five times greater than for a film of infinite lateral extent. On the other hand, the stress parallel to the stripe is not greatly affected and so the critical misfit strain for introduction of a transverse dislocation is approximately equal to that in an infinite film. These predictions are in reasonable agreement with experimental observations reported for Si1-xGex films grown on silicon mesa stripes.