Theoretical Study of the Stability of X@B₆ and X@B₁₂ Clusters: X=H–Br in Crystalline Silicon

Abstract

Ab initio calculations of the atomic and electronic structure of crystalline silicon (c-Si) with X@B 6 and X@B 12 (X ¼ H{Br) clusters have been performed to investigate carrier generation by doping atoms inside the cage of the boron clusters. We confirmed that octahedral B 6 , cubo-octahedral B 12 (B 12 -CO) and icosahedral B 12 (B 12 -ICO) can exist stably in c-Si and should act as double acceptors. We also found that H atoms can be settled in B 12 -CO clusters and the H@B 12 -CO cluster can introduce a very shallow single acceptor level whose activation energy is lower than those of B 6 , B 12 (-CO, -ICO) and substitutional boron atom (B s ). It is found on the basis of the formation energies that B@B 6 and B@B 12 will inevitably be formed and may degrade the efficiency of carrier generation. The H@B 12 -CO cluster is one of the most promising candidates as the cluster dopant for the improvement of the efficiency of boron implantation and the formation of a high-performance extremely shallow junction.