Structures and stabilities of boron clusters in silicon

An Empirical Tight Binding (ETB) model has been developed for boron in a tetrahedral environment, and subsequently applied in broad searches for B-2 and B-3 cluster structures in crystalline silicon. B-2 clusters with both boron atoms in substitutional sites were found to be very stable, but no further energy reduction was observed after adding a third B atom on an adjacent substitutional site. Formation energies and entropy arguments together suggest that B-2 substitutional clusters are much more plentiful than B-3 substitutional clusters. B-2 and B-3 clusters involving a single interstitial atom were found to be very stable, and several such structures are described. The most stable of these is the neutral 111-split interstitial B-2 cluster. As a rule, B-S was observed to be more stable than B-i as a cluster constituent, and clusters with the B atoms bonded together (BSBSI) appear to be more stable than those in which the B atoms are linked only through a self-interstitial (BSIBS).