A theoretical modelling of the oxygen
diffusivity in silicon and germanium crystals both at normal and high
hydrostatic pressure has been carried out using molecular mechanics,
semiempirical and ab initio methods. It was established that the diffusion process
of an interstitial oxygen atom (Oi) is controlled by the optimum configuration
of three silicon (germanium) atoms nearest to Oi. The calculated values of the
activation energy ΔEa(Si) = 2.59 eV, ΔEa(Ge) = 2.05 eV and pre-exponential
factor D0(Si) = 0.28 cm2 s−1, D0(Ge) = 0.39 cm2 s−1 are in good agreement with
experimental ones and for the first time describe perfectly the experimental
temperature dependence of the Oi diffusion constant in Si crystals (T =
350–1200 °C). Hydrostatic pressure (P≤80 kbar) results in a linear decrease of the diffusion
barrier (\partial_P \Delta E_{\mathrm {a}} (P)=-4.38\times 10^{-3}~{\mathrm
{eV~kbar^{-1}}} for Si crystals). The
calculated pressure dependence of Oi diffusivity in silicon crystals agrees
well with the pressure-enhanced initial growth of oxygen-related thermal
donors.
Source:IOPscience
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