Optical and electrical properties of pure and rare-earth-doped nc-Si/SiO2 composites prepared by RF cosputtering

Photoluminescence and optical absorption spectra from silicon nanoparticles embedded in SiO2 are presented. The material was synthesized by RF cosputtering. The samples were prepared with a variety of Si volume concentrations and annealing temperatures. The results are discussed by correlating them with the preparation conditions, the nanostructure, and comparing them with the results obtained for porous silicon. The conductivity, photoconductivity and minority carriers diffusion length were also obtained for samples with different Si content and average size of the nanostructure. The study gives information about the percolation threshold and the electrical transport mechanisms in the composite. Eu- and Er-doped samples were finally prepared and studied for their PL response. A clear correlation between the enhancement of the Er+3 infrared emission and the presence of the silicon nanostructure is shown. In the case of Eu-doped samples, emissions from Eu+3 or Eu+2 are observed depending on the characteristics of the host (when exciting with 514.5 nm laser radiation). Degenerate four-wave mixing signals suggest a strong interaction between the free carriers of the silicon nanostructure and the Eu ions that can promote the emission from Eu+2 under illumination.