Calculations were made of intrinsic vacancy and interstitial diffusivities using order (N) tight-binding simulations. Vacancy diffusion was found to occur with a diffusivity of about 10-4cm2/s at 900 to 1200C. Interstitial diffusion was found to be a factor of 10 to 100 times slower, and of the order of 10-5cm2/s for the same temperature range. These diffusivities were of the same order of magnitude as those predicted by previous molecular dynamics calculations performed using classical and Car-Parrinello models. Interstitial diffusion occurred via two different paths; one involving the motion of a single interstitial down the open (110) channels in the lattice, and another involving an intermediate (110) split interstitial which facilitated interstitial crossing from one (110) channel to another. Within the tight-binding model used, the split interstitial path was more important than the drift of a single interstitial at higher temperatures (above 1000C). The reverse was true below this temperature with little, if any, formation of split interstitials and diffusion which was dominated by traverse down the open channels of the lattice. Local density approximation data showed that the energetic advantage of the split interstitial over the tetrahedral interstitial was smaller than previously calculated; supporting the tight-binding results. The split interstitials were found to be relatively long-lived (lifetime sometimes in excess of 15ps) even in a potential that favored tetrahedral interstitial formation.

An Order(N) Tight-Binding Molecular Dynamics Study of Intrinsic Defect Diffusion in Silicon. Roberts, B.W., Luo, W., Johnson, K.A., Clancy, P.: Chemical Engineering Journal, 1999, 74[1-2], 67-75