Photoluminescence decay properties of Si-rich-oxide/SiO2 multilayer films with different Si-quantum dots densities

In this work, Si-rich-oxide/SiO2 multilayer films have been deposited by adjusting the radio-frequency power in a PECVD system, and Si quantum dots (Si-QDs) are obtained in the Si-rich-oxide layer after annealing treatment. FTIR results show that phase separation between Si and SiO2 occurs after annealing treatment. TEM and Raman spectra show that the size and density of Si-QDs are larger for the multilayer films deposited at 20 W. Compared with the film deposited at 40 W, a 1.7 times PL enhancement is obtained for the film deposited at 20 W, and the PL peak shifts toward low energy. Time-resolved PL spectra show the PL decay for the film deposited at 40 W can be expressed by the multi-exponential decay model, while stretched-exponential decay model can be used to describe the carrier recombination process when the density of Si-QDs is high enough. The PL decay time increases with the red shift of wavelength firstly and decreases, which suggests that quantum confinement effect is the main PL mechanism in the short wavelength region, and localized state transition in Si clusters contributes to the optical emission in the longer wavelength region. The results are further confirmed by low temperature PL spectra.