Atomic structure of B-related defects and B diffusion in Si predoped with P impurities

Abstract

We perform first-principles pseudopotential calculations to investigate the atomic structure and energetics of various defects consisting of B and P impurities and the effect of P on B diffusion in Si. In the equilibrium case, we find that a B-P pair is energetically most stable when P is positioned at a second-neighbor site of B. When excess Si interstitials are generated by implantation, B and P impurities tend to form I-s-B-P complexes with self-interstitials (I-s), where P still prefers to a second-neighbor site of B, particularly for high donor concentrations. Using the nudged elastic band method, we examine the diffusion of B and its energy barrier in the presence of P. We find that the diffusion pathways of B are similar to those reported for the I-s-B pair without P; however, the migration energy for B diffusion from the I-s-B-P complex increases by about 0.2 eV. The increase of the activation energy and the formation of the B-P pair acting as a trap for B diffusion provide a clue for understanding the suppression of B diffusion observed in Si predoped heavily with donor impurities.