Annealing atmosphere effects on the surface properties of Cd2SnO4 thin films obtained by RF sputtering

Abstract

Cd2SnO4 (CTO) thin films were prepared by RF sputtering technique from a CTO target and then annealed under Ar or Ar/CdS atmosphere. The detailed characterizations on the surface properties of as-deposited, Ar-annealed, and Ar/CdS-annealed CTO thin films were carried out by AFM, XPS, UPS, etc. The surface properties of the films are greatly dependent on the annealing atmosphere. Ar/CdS atmosphere promotes the grains to grow but slightly increases the surface roughness. Cadmium atoms sublimated off the CTO thin films during the annealing process and this sublimation can be suppressed under Ar/CdS atmosphere, which causes the surface of CTO thin films not homogeneous as inside. The fundamental band gap is determined to be 2.83eV. The Fermi level position is 1.7eV above the valence band maximum for the as-deposited films, while it shifts to 2.98eV and 3.21eV for the films annealed in Ar and Ar/CdS atmospheres, respectively. Work function for the Ar/CdS-annealed films is about 0.16eV higher than the Ar-annealed ones. These results could be used to design high efficiency thin film solar cells and water photolysis devices, in which the efficiency is sensitive to the surface properties of TCO thin films.