Atomistic study of structural metastability in coherently strained Si-like layers

Comparison of experimental values for critical mismatch of coherently strained semiconductor films with the predictions of equilibrium theories suggests that metastable structures with much greater critical mismatch than predicted by equilibrium theory can often be grown in practice. One possible mechanism for loss of coherence in such metastable structures is the generation of misfit dislocations in an initially perfect overlayer by nucleation of half-loop of misfit dislocation at the surface of the strained layer. The mismatch threshold for zero-temperature loss of coherence associated with this half-loop dislocation nucleation mechanism, which does not occur in the continuum model, is calculated using atomistic Monte Carlo techniques on a coherently strained layer composed of a model siliconlike material. The instability threshold for a 10-A{}-thick layer is found to be 11.2%, compared to the equilibrium critical mismatch of about 4%. Possible extensions of this approach to the problem of practical stability of coherently strained structures are discussed.