X-ray photoelectron spectroscopy study and humidity sensing properties of Zn doped SnO₂ thin films

Undoped and Zn-doped SnO₂ thin films are deposited onto glass substrates by sol–gel spin coating method. All the films are characterized by X-ray photon spectroscopy (XPS) and Fourier transform infra-red spectroscopy (FTIR). XPS shows that Sn presence as valence of Sn⁴⁺ in the prepared SnO₂ thin films instead of Sn²⁺. In addition, it also exhibits the amount of Zn in SnO₂ thin films, which increases with increasing Zn doping percentage. The Zn (2P_3/2) peak is symmetric and centred at around 1,021.73 eV which shifts to the lower binding energy of 1,020.83 eV for 15 at.% Zn doped SnO₂ thin film. FTIR study is used to describe the local environment of undoped and Zn-doped SnO₂ thin films which also confirms the synthesis of undoped and Zn-doped SnO₂ thin films. It is found that the resistance of SnO₂ thin films increases as Zn doping concentration increases at room humidity. The resistance of all the samples increases as relative humidity (RH) increases. The sensitivity of SnO₂ thin films increases as RH increases while it decreases as Zn doping percentage increases. Response time of SnO₂ thin film decreases as Zn doping percentage increases and recovery time slightly increases with doping percentage.