Self-trapped excitons on the surface of Si nanocrystals in SiO2

Abstract

The experimental data recently obtained by the femtosecond pump-probe spectroscopy technique have shown that the self-trapped exciton (STE) state plays a key role in the dynamics of hot excitons in photoexcited silicon nanocrystals embedded in a SiO matrix. We present a theoretical model of excitons self-trapped on Si–O bounds at the silicon nanocrystal surface. The thermally activated transition from the STE state to the nanocrystal has been studied. The nonradiative multiphonon recombination of the STE initiated by the interaction with vibrations of local dipoles in a amorphous SiO matrix has been considered, too. The relaxation process of “hot” carriers localized in Si nanocrystals has been modulated using Monte Carlo simulation. We have demonstrated that effective exchange between the STE states and “hot” free exciton states opens the new way of the energy relaxation and leads to the wide energy distribution of the hot carriers during 10–100 ps after excitation.