A comprehensive study on the migration of di- and tri-interstitials in Si was performed using classical molecular dynamics simulations with the Stillinger-Weber potential. At first the structure and energetics of the di- and the tri-interstitial were investigated, and the accuracy of the interatomic potential was tested by comparing the results with literature data obtained by tight-binding and density-functional-theory calculations. Then the migration was investigated between 800 and 1600K. Very long simulation times, large computational cells and different initial conditions were considered. The defect diffusivity, the self-diffusion coefficient per defect and the corresponding effective migration barriers were calculated. Compared to the mono-interstitial, the di-interstitial migrates faster, whereas the tri-interstitial diffused slower. The mobility of the di- and the mono-interstitial was higher than the mobility of the lattice atoms during the diffusion of these defects. On the other hand, the tri-interstitial mobility was lower than the corresponding atomic mobility. The migration mechanism of the di-interstitial showed a pronounced dependence on the temperature. At low temperature a high mobility on zig-zag-like lines along a <110> axis within a {110} plane was found, whereas the change between equivalent <110> directions or equivalent {110} planes occurred seldom and required a long time. At high temperature a frequent change between equivalent <110> directions or {110} planes was observed. During the diffusion within {110} planes the di-interstitial moves like a wave packet so that the atomic mobility was lower than that of the defect. On the other hand, the change between equivalent {110} migration planes was characterized by frequent atomic rearrangements. The visual analysis of the tri-interstitial diffusion revealed complex migration mechanisms and a high atomic mobility. The diffusivities and effective migration barriers obtained were compared with the few data from the literature.

Atomistic Study of the Migration of Di- and Tri-Interstitials in Silicon. M.Posselt, F.Gao, D.Zwicker: Physical Review B, 2005, 71[24], 245202 (12pp)