Diffusion of interstitial Hydrogen molecules in Crystalline Germanium and Silicon: Quantumchemical simulation

A theoretical modeling of the diffusivity of interstitial hydrogen molecules in germanium and silicon crystals has been carried out using quantumchemical method. It was established that the diffusion process of an interstitial hydrogen molecule is a thermally activated process over potential barrier that is additionally subjected to fluctuations caused by rotation of the hydrogen molecule. The calculated values of the activation energy ΔEa(Si)=0.79–0.83 eV, ΔEa(Ge)=0.58–0.63 eV and pre-exponential factor D0(Si)=7.4×10−4 cm2 s−1, D0(Ge)=6.5×10−4 cm2 s−1 are in an excellent agreement with experimental ones and for the first time describe perfectly an experimental temperature dependence of hydrogen molecules diffusion constant in Si crystals (T=100–300 °C). The influence of hydrostatic pressure on the activation energy of diffusion has been analyzed also.