INJECTION OF NONEQUILIBRIUM POINT-DEFECTS DURING DIFFUSION OF IMPURITIES IN CRYSTALS WITH A MIXED SELF-DIFFUSION MECHANISM

An analysis is made of the migration of a substitutional impurity by diffusion between interstices in a crystal with a mixed self-diffusion mechanism. The criteria for a deviation from an equilibrium distribution of point defects are obtained. Expressions for the coefficient of injection of nonequilibrium host interstices into the bulk of a crystal and for a nonlocal concentration-dependent diffusion coefficient are derived. It is shown that vacancy self-diffusion is important only when the vacancy component is fairly large, i.e., when it is comparable or greater than the interstitial component of self-diffusion. The influence of vancany self-diffusion is limited only by the surface layers, whereas in the bulk of a crystal the migrating vacancies recombine with the injected host interstices and have no significant influence on the impurity diffusion. When the concentration and mobility of an impurity are high, its diffusion is governed not so much by the actual characteristics of this impurity as by the rate of formation of vacant sites in the crystal lattice because of the arrival of vacancies or because of escape of excess host interstices to surface sinks. It is suggested that profiles of the reciprocal of the impurity concentration can facilitate an analysis of the self-diffusion mechanism. These profiles give rise to near-linear dependences of the reciprocal concentration on the distance from the boundary (surface). When the contribution of the vacancy component is large, the linear region shifts into the bulk of a crystal because of accelerated diffusion associated with the arrival of vacancies. The interstitial and vacancy self-diffusion coefficients can be determined from the slopes of these dependences and from the magnitude of its shift.