Kinetic approach to multiple pathway diffusion with traps.

Abstract

Multiple pathway diffusion with traps was analyzed in the kinetic approach in which the diffusion terms in the diffusion-kinetic equations are replaced by kinetic ones. The criteria for applicability of the kinetic approach are discussed. Since the solutions are linear combinations of exponents, both the exponents and the preexponential factors were taken into account. As an example Au diffusion into a Si film was studied taking into account both the dissociative and the kickout mechanisms. To analyze thin-film diffusion, in addition to terms describing the diffusion transport in crystals of infinite sizes, thin-film surfaces were considered as a substantial source and/or sink of point defects. The different diffusion mechanisms and regimes and the conditions of transition from one mechanism and/or regime to another were found. Expressions were obtained for the critical sample thicknesses, dislocation density, swirl and vacancy cluster density, and temperatures, when transitions of the diffusion transport mechanisms and regimes occur. Possible areas for existence of these transport regimes were determined. Quantitative criteria of the critical values of temperature, dislocation density and thin film thickness for transitions of the Au-Si diffusion transport mechanisms were obtained. For fairly long times the results obtained in the kinetic approach coincide with those of the diffusion-kinetic one but the set of pure kinetic equations is much simpler to solve. This implies that the kinetic approach is a valuable approximation to multiple pathway diffusion with traps.