Structure and optical properties of amorphous SiOx thin films prepared by co-evaporation of Si and SiO

Amorphous SiOx (0.47≤x≤0.95) thin films were prepared by co-evaporation of Si and SiO in ultrahigh vacuum onto silicon substrates maintained at 100°C. A strong improvement of the photoluminescence intensity can be observed simultaneously with a redshift up to an annealing temperature in the range 500–650°C. For higher annealing temperatures, the PL strongly decreases. Composition and structure investigations were performed by infrared and Raman spectrometry experiments on films annealed at different temperatures. These two techniques show that a-Si clusters appear in the matrix of SiOx. The optical gap of the films was measured as a function of the composition and of the annealing temperature. For all the samples, the gap increases with increasing x. With annealing treatments, there is a first increase of the gap followed by a decrease when the annealing temperature is more than 500°C. This evolution could be explained by the presence of silicon clusters in the films.