Recent experimental studies [
A. Ural, P. B. Griffin, and J. D. Plummer, J. Appl. Phys. 85, 6440 (1999)
R. Kim, T. Hirose, T. Shano, H. Tsuji, and K. Taniguchi, Jpn. J. Appl. Phys. 41, 227 (2002)
S. Solmi, M. Ferri, M. Bersani, D. Giubertoni, and V. Soncini, J. Appl. Phys. 94, 4950 (2003)
] have suggested the importance of Si interstitials in As transient enhanced diffusion during pn junction formation in silicon. Using density functional theory calculations within the generalized gradient approximation, we have examined the structure, stability and diffusion of As–Sii pairs. For the negatively charged As–Sii pair, we find a minimum energy structure in which the As atom bridges two approximate lattice Si atoms, while for the neutral and positively charged As–Sii we find the lowest energy structure is comprised of an As and Sii pair that is aligned in the  direction while sharing a lattice site. Our results suggest that in n-type extrinsic regions the diffusion of −1 charged As–Sii pairs will be prevailing with an overall activation energy of 3.1–3.4 eV, while under intrinsic conditions the neutral and −1 charged pairs will both contribute to arsenic diffusion. The predicted activation energies are similar to experimental observations for As diffusion and previous calculations for As-vacancy complex diffusion. These results clearly support that interstitials can contribute significantly to As transient enhanced diffusion, particularly in the region where interstitials exist in excess.