Low Resistivity Sputter Deposited SnOx Thin Films: An Indium-Free Transparent Conductive Oxide?

Abstract

This study investigates the influence of oxygen concentration and thermal treatment on the optical and electrical properties of tin oxide (SnOx) thin films deposited via radio frequency (RF) magnetron sputtering. The oxygen content in the sputtering process gas is systematically varied, revealing its critical role in influencing the films’ charge carrier density, mobility, and resistivity. Optimal conductivity (resistivity as low as 3.4 mΩ cm) is achieved at an argon-oxygen mix gas flow rate of 3.4 sccm combined with quasi-in-situ heating, enhancing both charge carrier density and mobility. Optical analysis revealed that transmittance and absorptance depend on oxygen flow. In the long-wavelength range, absorption scales with the number of free carriers, while in the short-wavelength range, discrete absorption peaks below the band gap were observed, possibly originating from a secondary SnO-like phase.