The migration of point defects in Si, and the corresponding atomic mobility, were investigated via comprehensive classical molecular-dynamics simulations, using the Stillinger-Weber potential and the Tersoff potential. In contrast to most previous studies, both the point defect diffusivity and the self-diffusion coefficient per defect were calculated separately so that the diffusion-correlation factor could be determined. Simulations involving both the Stillinger-Weber and the Tersoff potential showed that vacancy migration was characterized by transformation of the tetrahedral vacancy to the split vacancy and vice versa and that the diffusion-correlation factor, fV, was about 0.5. This value was also derived by using statistical diffusion theory under the assumption of the same migration mechanism. The mechanisms of self-interstitial migration were more complex. The detailed study, including a visual analysis and investigations using the nudged elastic band method, revealed a variety of transformations between various self-interstitial configurations. Molecular dynamics simulations, using the Stillinger-Weber potential, showed that the self-interstitial migration was dominated by a dumb-bell mechanism whereas, in the case of the Tersoff potential, the interstitialcy mechanism prevailed. The corresponding values of the correlation factor, fI, were different, giving 0.59 and 0.69 for the dumb-bell and the interstitialcy mechanisms, respectively. The latter value was nearly equal to that obtained by the statistical theory, which assumed the interstitialcy mechanism. Recent analysis of experimental results demonstrated that, within the framework of state-of-the-art diffusion and reaction models, the best interpretation of point defect data could be given by assuming that fI was about 0.6. A comparison with the present atomistic study led to the conclusion that self-interstitial migration in Si should be governed by a dumb-bell mechanism.

Correlation between Self-Diffusion in Si and the Migration Mechanisms of Vacancies and Self-Interstitials - an Atomistic Study. M.Posselt, F.Gao, H.Bracht: Physical Review B, 2008, 78[3], 035208 (9pp)