Structural and optical properties of the B doped, P doped and B-P codoped silicon nanocrystals have been investigated
using first-principles calculations. It was found that the codoped system tends to reduce structure distortion around B/P
impurities compared with B/P single doped systems and shows a decreased energy band gap compared with undoped
system due to there being electronic compensating effect. In addition, the spatial behaviors of density of states indicated
that codoping possesses a tendency of confining the electrons and holes around the B/P impurities, which suggests the
possibility of increasing electron emission transition rates between donor and acceptor. Moreover, the dielectric
functions calculation demonstrated that the optical absorption of codoped silicon nanocrystals have the characteristic of
the energy band gap being redshifted with respect to the undoped case together with peak appearing at lower energy side.