AB-INITIO PSEUDOPOTENTIAL CALCULATIONS OF B DIFFUSION AND PAIRING IN SI

The ab initio pseudopotential method was used to study the boron diffu sion and pairing process in crystalline silicon. The results show that substitutional B attracts interstitial Si with a binding energy of 1. 1 +/- 0.1 eV. We show that B diffusion is significantly enhanced in th e presence of the Si interstitial due to the substantial lowering of t he migrational barrier through most likely a kick-out mechanism. The r esulting mobile boron can also be trapped by another substitutional bo ron with a binding energy of 1.8 +/- 0.1 eV, forming an immobile and e lectrically inactive two-boron pair along a (001) direction. It is als o found that the pairing of these two boron atoms involves the trappin g of a Si interstitial. Alternatively, two B pairs that do not trap th e Si interstitial were found to be energetically unfavorable. All of t hese findings are consistent with experimental results.