Optical excitation and emission processes of Si-QD/SiO2 multilayer films with different SiO2 layer thicknesses

Si-rich oxide/SiO₂ multilayer films with different SiO₂ layer thicknesses have been deposited by the plasma enhanced chemical vapor deposition technique, and crystallized Si quantum dot (Si-QD)/SiO₂ multilayer films are obtained after annealing at 1100 ^°C. The photoluminescence (PL) intensity of the multilayer films increases significantly with increasing SiO₂ layer thickness, and the PL peak shifts from 1.25 eV to 1.34 eV. The PL excitation spectra indicate that the maximal PL excitation intensity is located at 4.1 eV, and an excitation–transfer mechanism exists in the excitation processes. The PL decay time for a certain wavelength is a constant when the SiO₂ thickness is larger than 2 nm, and a slow PL decay process is obtained when the SiO₂ layer is 1 nm. In addition, the PL peak shifts toward high energy with decreasing temperature only when the SiO₂ layer is thick enough. Detailed analyses show that the mechanism of PL changes from the quantum confinement effect to interface defects with decreasing SiO₂ layer thickness.