Boron clusters in high-dose implanted silicon

The electronic structures and X-ray photoelectron spectra of silicon models with octahedral B, icosahedral B, or cubooctahedral B clusters are investigated using first-principles calculations. It is found that the B and B clusters act as double acceptors in silicon and that the simulated chemical shift of the B 1s orbital signals of the B and cubo-octahedral B 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 B and cubo-octahedral B 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. ©2007 The Japan Society of Applied Physics.