H2S gas sensing properties of nanocrystalline Cu-doped ZnO thin films prepared by advanced spray pyrolysis

The ZnO-based thin films doped with 1–4 wt% Cu were deposited on the glass substrates using the advanced spray pyrolysis technique. All films are deposited at 473 K. The crystallinity and morphology of the films were characterized by XRD, TEM and FE-SEM respectively. The structural analyses of the films indicate that they are polycrystalline and have a hexagonal wurtzite structure; however Cu doping enhances the preferential orientation along the [0 0 2]. The energy dispersive X-ray spectroscopic analysis (EDX) confirmed an enhancement in the amount of Cu in the film with increase in the copper concentration in the starting solution. The sensor response was estimated by the change in the electrical conductance of the film in the absence and presence of H2S gas. The sensor response and selectivity in relation to, operation temperature, Cu doping concentration and the gas concentration has been systematically studied. A significant response (∼0.38) towards 20 ppm H2S at 523 K operating temperature is observed for the 4 wt% Cu-doped ZnO. The Pd-sensitized 4 wt% Cu doped ZnO film exhibits improved sensing characteristics with good stability.