First-principles total-energy calculations of the atomic diffusion of group-V impurities revealed an effect of pressure upon the activation energy for diffusion. In the case of the vacancy mechanism, the activation energy for P decreased with pressure. In the case of the interstitial mechanism, the formation energy of the interstitial impurity exhibited a general tendency to increase with pressure. The microscopic origin of the pressure dependence was explained in terms of the local strains around defects. The negative pressure dependence which was common to the vacancy-mediated diffusion of group-V impurities could be explained by the peculiar properties of the isolated vacancy. These included a breathing distortion of surrounding Si atoms towards the vacancy site, giving rise to a tensile strain around the vacancy, and lattice distortions which originated from the vacancy and caused weak vacancy-impurity interactions. The positive pressure dependence of interstitial-mediated diffusion was closely related to the atomic structures of the interstitial impurities, which produced compressive strains in the surrounding Si-Si bonds.

O.Sugino, A.Oshiyama: Physical Review B, 1992, 46[19], 12335-41