Strain Relaxation by Misfit Dislocations

The mechanism of strain release in heteroepitaxial mismatched structures of semiconductors by misfit dislocations (MD) is still not well known. The so called equilibrium theories[1,2] correctly predict the critical film thickness above which pseudomorphic structures are no longer stable and misfit dislocations appear at the interface between film and substrate. However, above the critical thickness value the experimental rate of strain release as a function of the thickness is much lower than predicted by these theories. Some authors suggest that the measured strain may be greater than the predicted one since the system may be in a metastable equilibrium state because of the low rate of strain release at room temperature[3,4] or because the activation energy for the nucleation of new dislocations is not available[5]. However, experiments with samples having different misfit values and growth rates show that the residual strain is likely only to depend on the film thickness[6], so the samples should be close to a stable equilibrium state which should be different from the one depicted by the equilibrium theories.