Simulations of dopant clustering in silicon: Dimer calculations using DFT forces

We have carried out computer simulations to study the formation and break-up of boron clusters in crystalline silicon. Density functional theory was used to evaluate the interatomic interactions and dimer method used to find the mechanism and rate of the atomic rearrangement processes. The transition rates were calculated within harmonic transition state theory. The simulations have shown how the highly stable B₃I^- cluster in silicon can break up, both by a direct dissociation mechanism and by an interstitial mediated dissociation. The former has an activation energy of 4.3 eV, but the latter around 3.5 eV. The formation of the boron clusters is diffusion limited, i.e. attachment of boron interstitials involves lower barrier than diffusion. But, rearrangements of the boron clusters from one configuration to another turn out to have rather large activation barriers.