Critical Strain for Surface Nucleation of Dislocations in Silicon

TL;DR

This study combines energy barrier calculations and molecular dynamics simulations to show that surface features significantly lower the critical strain needed for dislocation nucleation in silicon, aligning models with experimental observations.

Contribution

It demonstrates that surface features like bent steps reduce the critical strain for dislocation nucleation, resolving discrepancies between experiments and atomistic models.

Findings

Surface features lower critical strain to 6.4% for shuffle dislocations.

Shuffle-glide dislocation complex critical strain is reduced to 5.3%.

Results are consistent across different interatomic potentials.

Abstract

A long-standing discrepancy exists between experiments and atomistic models concerning the critical strain needed for surface nucleation of dislocations in silicon-germanium systems. While dislocation nucleation is readily observed in hetero-epitaxial thin films with misfit strains less than 4%, existing atomistic models predict that a critical strain over 7.8% is needed to overcome the kinetic barrier for dislocation nucleation. Using zero-temperature energy barrier calculations and finite-temperature Molecular Dynamics simulations, we show that 3-dimensional surface features such as a sharply bent step can lower the predicted critical nucleation strain of a shuffle-set dislocation to 6.4%, and that of a shuffle-glide dislocation complex to 5.3%. Consistent findings are obtained using both the Stillinger-Weber (SW) and modified embedded-atom method (MEAM) potentials, providing support to the physical relevance of the shuffle-glide dislocation complex, which was previously considered as an artifact of the SW potential.