First-Principles Study of 2.2 nm Silicon Nanocrystals Doped with Boron

First-principles study of boron (B)-doped silicon nanocrystals (Si NCs) at 0 K in the framework of density functional theory has been carried out. It is found that B prefers residing at the surface of Si NCs, similar to phosphorus (P). Different from P, B induces surface restructuring when B is one- or two-coordinated at the NC surface. B doping does not significantly change the bandgap of Si NCs, but in most cases B introduces deep energy levels in the bandgap of Si NCs. This explains the B-doping induced quenching of band-edge light emission usually observed in experiments. The negligible infrared absorption of B-doped Si NCs may result from the fact that only three-coordinated B is formed at the NC surface. The electronic transitions involving the energy levels induced by these three-coordinated B are not in the infrared range.