Threshold energy reduction for carrier multiplication in Si-QDs by phosphorus doping

The Si-QDs/SiO2 multilayer films with phosphorus (P) doping have been prepared, and carrier multiplication effect of the films with and without P doping was investigated by relative quantum yield of photoluminescence (PL). The relative quantum yield of PL shows a step like increase when the excitation energy is larger than 2Eg of Si-QDs, and the carrier multiplication is caused by space-separated quantum cutting in adjacent QDs. The PL peak shifts toward high energy region after P-doping, and the PL intensity is enhanced, however, the threshold energy for carrier multiplication is decreased from 2.97 to 2.89 eV. The results suggest that non-radiative recombination at the surface of Si-QDs is suppressed by P passivation, and radiative recombination from conduction band to surface defect level is possible. Energy transfer from hot electron-hole pair to surface defect level leads to the optical excitation of defect level, which generates an extra electron-hole pair, and carrier multiplication effect is observed in the P-doped multilayer film with lower excitation energy.