  The theoretical analysis of the process of diffusion of interstitial oxygen
atoms and hydrogen molecules in silicon and germanium crystals has been
performed. The calculated values of the activation energy and pre-exponential
factor for an interstitial oxygen atom Ea(Si) = 2.59 eV, Ea(Ge) = 2.05 eV,
D(Si)= 0.28 cm2s-1, D(Ge)= 0.39 cm2s-1 and interstitial hydrogen molecule
Ea(Si) = 0.79-0.83 eV, Ea(Ge) = 0.58-0.62 eV, D(Si)= 7.4 10(-4) cm2s-1, D(Ge)=
6.5 10(-4) cm2s-1 are in an excellent agreement with experimental ones and for
the first time describe perfectly an experimental temperature dependence of an
interstitial oxygen atom and hydrogen molecules diffusion constant in Si and Ge
crystals. It is shown, that for a case of impurity atom with a strong
interaction with a lattice (interstitial oxygen atom) process of diffusion has
a cooperative nature - the activation energy and pre-exponential are controlled
by the optimum position of three nearest lattice atoms. For a case of extended
defect with a weak interaction (an interstitial hydrogen molecule) process of
diffusion is determined by the activation barrier subjected to fluctuations
connected with rotation of a hydrogen molecule. The effect of hydrostatic
pressure on the process of diffusion is discussed also.
