Evidence of light-emitting amorphous silicon clusters confined in a silicon oxide matrix

Amorphous silicon oxide thin films were prepared by the coevaporation technique in ultrahigh vacuum. Different compositions were obtained by changing the evaporation rate of silicon. The samples were then annealed to different temperatures up to 950 °C. The composition and the structure were investigated using energy dispersive x-ray spectroscopy, infrared absorption measurements, and Raman spectroscopy. This study attests the presence of amorphous silicon clusters in a silicon oxide matrix. Optical transmission measurements were performed and interpreted in the field of the composite medium theory. The obtained results are in good agreement with the presented structural model. The photoluminescence in the red-orange domain was studied in relation with the structure. The correlation between the photoluminescence energy and intensity and the structure shows that the light emission originates from the silicon clusters embedded in the silicon oxide matrix. Moreover the dependence of the photoluminescence energy with the silicon volume fraction suggests the origin of the light emission could be due to a quantum confinement effect of carriers in the amorphous silicon clusters.