Photoluminescence of Si-Rich SiO2 Films: Si Clusters as Luminescent Centers

Si-rich SiO2 films have been prepared by a rf cosputtering method and their photoluminescence, as well as infrared absorption and Raman spectra, has been measured for the as-deposited and annealed films. Photoluminescence spectra very similar to those of porous Si were observed for the sample with a relatively low Si content. Redshift of the luminescence peak was observed upon annealing. Results of infrared and Raman measurements strongly suggest that Si clusters are embedded in the as-deposited sample, and that their size increases upon annealing. The photoluminescence is thus thought to arise from the Si clusters, in which the gap between the highest-occupied and lowest-unoccupied molecular orbitals decreases as the size increases, causing the redshift of the photoluminescence peak. A sample containing well-grown Si microcrystals was also prepared by increasing the Si content. No detectable photoluminescence signal was observed for this sample.