Boron Clusters in High-Dose Implanted Silicon

Abstract

The electronic structures and X-ray photoelectron spectra of silicon models with octahedral B6, icosahedral B12, or cubo-octahedral B12 clusters are investigated using first-principles calculations. It is found that the B6 and B12 clusters act as double acceptors in silicon and that the simulated chemical shift of the B 1s orbital signals of the B6 and cubo-octahedral B12 clusters in X-ray photoelectron spectra coincides exactly with the chemical shift of B 1s experimentally observed in as-implanted silicon at an extremely high dose of boron. These results reveal that the B6 and cubo-octahedral B12 clusters are the origin of hole carriers in silicon. We propose a mechanism for hole generation and a physical model for boron cluster formation at implantation-induced divacancy sites and multi vacancy sites.