H2S gas sensing properties of undoped and Ti doped ZnO thin films deposited by chemical spray pyrolysis

Abstract

Undoped and Ti doped ZnO thin films were successfully grown on glass substrates by the chemical spray pyrolysis method. The effect of Ti doping on the structural, surface morphology, elemental composition, photoluminescence and H2S gas sensing properties of these films were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectrometer (EDX), photoluminescence (PL) and gas analyzer measurements, respectively. XRD analyses confirm that the films are polycrystalline zinc oxide with the hexagonal wurtzite structure, and the 2 wt% Ti doping results into the optimum crystallinity. FE-SEM analyses assist the XRD observations, and show polygonal granular surface morphology for 2 wt% Ti doped ZnO films with large grain size amongst all films. The room temperature PL studies revealed a broad green PL band along with a relatively weak UV band for all the films, which corresponds to oxygen vacancies and near-band-edge emission (NBE), respectively. The H2S gas sensing properties of all the films are studied as a function of operating temperature, Ti doping concentration and H2S gas concentration. Finally, the selective behaviour of the optimized TZO film towards H2S gas was tested against different organic gases. The 2 wt% Ti doped ZnO thin film exhibits maximum gas response (∼0.29) to 20 ppm H2S gas exposure at 200 °C operating temperature and demonstrates a good selectivity over other organic gases.