Visible photoluminescence in amorphous SiOx thin films prepared by silicon evaporation under a molecular oxygen atmosphere

A simple reactive evaporation method is proposed to prepare light-emitting amorphous ${\mathrm{SiO}}_x$ thin films. By evaporating pure silicon in a controlled molecular oxygen atmosphere, it is possible to obtain a very large composition range. By changing the pressure in the preparation chamber, x can be varied from 0.7 to 1.85. The composition and the structure of the films were investigated using energy dispersive x-ray, infrared absorption and x-ray photoelectron spectroscopies. The samples contain amorphous silicon clusters dispersed inside an insulating silicon oxide matrix. The room-temperature photoluminescence properties were then measured. By conveniently choosing the oxygen pressure, the as-deposited films exhibit visible photoluminescence without any annealing post-treatments. The luminescence intensity initially increases with excess silicon concentration and then disappears for a too-high silicon excess. The above effect is interpreted in terms of confinement of the amorphous silicon clusters in the insulating matrix.