The  ab initio  pseudopotential method was used to study B diffusion and pairing in crystalline samples. The results showed that substitutional B attracted interstitial Si with a binding energy of 1.1eV. It was shown that B diffusion was significantly enhanced, in the presence of the Si interstitial, due to a substantial lowering of the migrational barrier; arising probably from a kick-out mechanism. The resultant mobile B could also be trapped by another substitutional B with a binding energy of 1.8eV. This led to the formation of an immobile and electrically inactive 2-B pair along a <001> direction. It was also found that the pairing of these two B atoms involved the trapping of a Si interstitial. On the other hand, two B pairs that did not trap a Si interstitial were found to be energetically unfavorable. All of the results were consistent with experimental results.

Ab initio Pseudopotential Calculations of B Diffusion and Pairing in Si. J.Zhu, T.Diaz de la Rubia, L.H.Yang, C.Mailhiot, G.H.Gilmer: Physical Review B, 1996, 54[7], 4741-7