Empirical molecular-dynamics study of diffusion in liquid semiconductors.

We report the results of an extensive molecular-dynamics study of diffusion in liquid Si and Ge ( l -Si and l -Ge! and of impurities in l -Ge, using empirical Stillinger-Weber ~SW! potentials with several choices of parameters. We use a numerical algorithm in which the three-body part of the SW potential is decomposed into products of two-body potentials, thereby permitting the study of large systems. One choice of SW parameters agrees very well with the observed l -Ge structure factors. The diffusion coefficients D(T) at melting are found to be approximately 6.4310 cm/s for l -Si, in good agreement with previous calculations, and about 4.2310 and 4.6310 cm/s for two models of l -Ge. In all cases, D(T) can be fitted to an activated temperature dependence, with activation energies Ed of about 0.42 eV for l -Si, and 0.32 or 0.26 eV for two models of l -Ge, as calculated from either the Einstein relation or from a Green-Kubo-type integration of the velocity autocorrelation function. D(T) for Si impurities in l -Ge is found to be very similar to the selfdiffusion coefficient of l -Ge. We briefly discuss possible reasons why the SW potentials give D(T)’s substantially lower than ab initio predictions. @S0163-1829~96!03644-2#