Unusual enhancement in electrical conductivity of tin oxide thin films with zinc doping

Electrical conductivity of SnO2-based oxides is of great importance for their application as transparent conducting oxides (TCO) and gas sensors. In this paper, for the first time, an unusual enhancement in electrical conductivity was observed for SnO2 films upon zinc doping. Films with Zn/(Zn + Sn) reaching 0.48 were grown by pulsed spray-evaporation chemical vapor deposition. X-Ray diffraction (XRD) shows that pure and zinc-doped SnO2 films grow in the tetragonal rutile-type structure. Within the low doping concentration range, Zn leads to a significant decrease of the crystallite size and electrical resistivity. Increasing Zn doping concentration above Zn/(Zn + Sn) = 0.12 leads to an XRD-amorphous film with electrical resistivity below 0.015 Ω cm at room temperature. Optical measurements show transparencies above 80% in the visible spectral range for all films, and doping was shown to be efficient for the band gap tuning.