Iron–acceptor pairs in silicon: Structure and formation processes

We performed a theoretical investigation on the properties of iron–acceptor impurity pairs (Fe–A, with A=B, Al, Ga, and In) in silicon. The calculations were performed within the framework of an ionic model, including elastic and electrostatic interactions. In contrast to the conventional point charge ionic model, our model includes a correction to the electrostatic interaction that takes into account the valence electronic cloud polarization, which adds a short range, attractive interaction to Fe–A pair bonding, and includes the silicon lattice relaxation due to the atomic size difference between the acceptor and the lattice atoms. Our results are in good agreement with the experimental trends among the Fe–A pairs, describing the increase in the pair donor energy level with increasing A principal quantum number and decreasing pair separation distance, and the pair configurational symmetries.