Strain effect on self-diffusion in silicon: Numerical study

We present here a numerical study of the self-diffusion mechanisms in silicon using a semiempirical Stillinger-Weber potential to calculate formation and migration energies and entropies. We find that self-diffusion in bulk Si is mediated by vacancies at low temperature, but that interstitials play a more and more important role when temperature increases, in agreement with recent experimental data. This behavior is shown to strongly evolve under biaxial strain (epsilon) which simulates the effect of epitaxial growth of a Si thin film. Our methodology allows us to classify vacancy vs interstitial self-diffusion within a (T,epsilon) diagram, which reveals a transition from vacancy toward interstitial diffusion at low temperature beyond a critical tensile strain which corresponds to Si/Ge size mismatch.