Lightly boron and phosphorus co-doped silicon nanocrystals.

The co-doping of silicon nanocrystals (Si NCs) with boron (B) and phosphorus (P) is an important means to tune the optical properties of Si NCs. However, all the previous work only concerns heavy co-doping. In this study, we carry out first-principles study on light co-doping that leads to the incorporation of dopants at the NC surface, rather than inside NCs. The size (diameter) of Si NCs currently investigated is ~2.2 nm. A Si NC without doping is in the form of SiH. It is found that the formation energy of a lightly co-doped Si NC is between those of B- and P-doped Si NCs, hardly being affected by the distance between dopants. Electron localization around P is mainly responsible for the light co-doping-induced reduction of the bandgap of Si NCs. The redshifts of excitation- and emission-energy induced by light co-doping is slightly larger than those induced by B and P doping in most cases. The band-edge radiative recombination rates of undoped, B-doped, P-doped, and lightly co-doped Si NCs have been compared. [ABSTRACT FROM AUTHOR]