Theory of Diffusion and Equilibrium Position of Interstitial Impurities in the Diamond Lattice

Abstract

A theory is developed for diffusion of interstitial impurities in the diamond lattice. For ionized impurities the theory is based on a model in which the interaction of the ion with the host atoms is given by an attractive potential produced by the polarization of the host atoms, and a repulsive potential due to overlap of nonbonding electrons. The interaction energy is calculated at two interstitial positions of symmetry, and the activation energy for diffusion is taken as the difference between the two. Good agreement with experiment is found for lithium, copper, and silver. The theory predicts an optimum impurity size for diffusion, and thus explains the great diffusivity of copper. It also claims that the interstitial position of lithium and copper is not one of tetrahedral symmetry.