Phosphorus and boron codoping of silicon nanocrystals by ion implantation: Photoluminescence properties

The photoluminescence (PL) properties of P or B single-doped Si nanocrystals (Si-nc's) and P and B co-doped Si-nc's are studied. In the single-doped Si-nc samples, PL quenching occurs as a result of the Auger nonradiative recombination process between the photoexcited excitons and free carriers supplied by doped impurities. In the (P, B) co-doped sample, on the other hand, the donor-acceptor (D-A)-pair recombination emission is clearly observed on the long-wavelength side of the intrinsic Si-nc emission peak at similar to 900 nm. The D-A-pair recombination energy is found to be smaller than the band-gap energy of bulk Si and is strongly dependent on the number of P and B impurities doped in a Si-nc. PL spectra are measured at 50 and 300 K and found to indicate that strong thermal quenching occurs in a (P, B) co-doped sample at 300 K. This quenching effect is probably because of carrier migration among the donor and acceptor states. The PL decay rate is determined as a function of the emitted-light wavelength for the pure and (P, B) co-doped Si-nc samples.