Extensive first-principles total-energy calculations were presented for B-Si interstitial complexes with various configurations and charge states within the density functional theory. several stable and metastable configurations were found. It was also found that the stability of each configuration was sensitive to its charge state. The most stable configuration was a pair of a substitutional B and an interstitial Si for positively charged state, whereas an interstitialcy configuration was the most stable for negatively charged state. The pair and the interstitialcy configurations have almost same formation energies in their neutral charge states. Examination of electron states induced by the B-Si complexes indicated that the neutral interstitialcy configuration was an active center for electron spin resonance measurements. It was also found that the B-Si complex was a negative-U system in which neutral charge states were only metastable with the Fermi energy at any position in the energy gap, corroborating the earlier experimental finding by Watkins and collaborators. Diffusion pathways and corresponding activation energies for the B-Si complex were presented. It was found that the pathways and the activation energies were again sensitive to the charge state, opening a possibility of recombination enhanced diffusion.

Atomic and Electronic Structures of a Boron Impurity and its Diffusion Pathways in Crystalline Si. J.W.Jeong, A.Oshiyama: Physical Review B, 2001, 64[23], 235204 (9pp)