  The diffusion equation for nonequilibrium interstitial impurity atoms taking
into account their charge states and drift of all mobile interstitial species
in the built-in electric field and in the field of elastic stress was obtained.
The obtained generalized equation is equivalent to the set of diffusion
equations written for the interstitial impurity atoms in each individual charge
state. Due to a number of the characteristic features the generalized equation
is more convenient for numerical solution than the original system of separate
diffusion equations. On this basis, the macroscopic description of
stress-mediated impurity diffusion due to a kick-out mechanism was obtained. It
is supposed that the interstitial impurity atom makes a number of jumps before
conversion to the substitutional position. At the same time, a local
equilibrium prevails between substitutionally dissolved impurity atoms,
nonequilibrium self-interstitials, and interstitial impurity atoms. Also, the
derived equation for impurity diffusion due to the kick-out mechanism takes
into account all charge states of interstitial impurity atoms as well as drift
of interstitial species in the electric field and in the field of elastic
stress. Moreover, this equation exactly matches the equation of stress-mediated
impurity diffusion due to generation, migration, and dissociation of the
equilibrium pairs "impurity atom - self-interstitial".
