It was recalled that the vacancy-mediated diffusion of substitutional impurities depended markedly upon the nature of the impurity-vacancy interaction. An attractive interaction, which extended to at least the third-nearest neighbor, permitted a vacancy to move along a ring of Si sites around the impurity. This process permitted the impurity-vacancy pair to move, and was the basis of the ring mechanism for diffusion. In order to determine the importance of this mechanism for As, density functional calculations of As-vacancy interactions were carried out. Calculations were also made of the vacancy migration barriers on the circular path around the impurity. The binding energy of the As-V pair was found to be 1.17eV. This energy decreased to 0.36eV when the vacancy moved onto the third nearest-neighbor site; which was the most remote site on the ring path. It was found that the migration barriers to vacancy hopping around the impurity were an order of magnitude lower than those in bulk Si. The effective barrier along the ring path was therefore determined mainly by the difference in the binding energies on the first and third nearest-neighbor sites. It was estimated to be equal to about 0.81eV; in fairly good agreement with experiment. Monte Carlo simulation of As diffusion in Si was carried out by using  ab initio  binding energies and migration barriers. It was noted that, at temperatures ranging from 700 to 1300K, vacancy-assisted As diffusion was entirely dominated by the ring mechanism.

As-Vacancy Interaction and Ring Mechanism of Diffusion in Si. O.Pankratov, H.Huang, T.Diaz de la Rubia, C.Mailhiot: Physical Review B, 1997, 56[20], 13172-6