Study of silica–titania films doped with Er and Ag by RBS and ERDA

Abstract

The photoluminescence (PL) efficiency of Er-doped silica–titania planar waveguides, prepared by sol–gel processing, may be enhanced through the incorporation of neutral Ag metal particles. However, the presence of residual Si–OH groups and the limited reproducibility of the doping process limit the optical activity of the Er 3+ ions. We have used Rutherford backscattering spectrometry (RBS) combined with elastic recoil detection analysis (ERDA) to study the incorporation behaviour of Ag and H atoms during the heat treatments used to densify the films. These were deposited by sol–gel spin-coating on single crystal Si or silica-buffered Si substrates (∼5 μm thick silica buffer layer). The results indicate a homogeneous distribution of Er in the as-deposited films. On the contrary, Ag displays a bimodal in-depth profile centred at the film surface and at the film/substrate interface. Annealing up to 700 °C leads to in-diffusion and concentration of all the Ag species at the latter interface. The H concentration maintains nearly the same values after annealing at 500 and 900 °C, with larger values for temperatures in between. During heat treatment the Er profile remains stable.