Piezoelectricity and Visible Light Luminescence in Tetravalent-Metal-Doped Poled Silica Thin Films

Abstract

It is known that poling treatment in germanium-doped silica (Ge:SiO₂) glass raises their optical nonlinearity and produces the Pockels effect. This means that the poling treatment in Ge:SiO₂ produces asymmetricity in the glass. We generated piezoelectricity in poled Ge:SiO₂ glass thin films. Tetravalent-metal-doped SiO₂ (M⁴⁺:SiO₂) films were prepared on Si substrates by RF magnetron sputtering. We used germanium, titanium, and tin as doping materials. However, less than a week later, piezoelectricity disappeared almost completely in all the samples. To prevent piezoelectricity from disappearing, we attempted to pin the doping ions. We developed a pinning technique based on the superstructure of a Ge-Ti-Sn:SiO₂ and Ge-Ti-Zr:SiO₂. The superstructure was very effective in preventing piezoelectricity from disappearing. Furthermore, broadband visible light emission was observed in the proposed superstructure film.