Characterization and NO2 gas sensing performance of CdO:In2O3 polycrystalline thin films prepared by spray pyrolysis technique

Polycrystalline CdO:In2O3 thin films for gas sensor applications were prepared on glass and silicon substrates by using one-step spray pyrolysis technique from the aqueous solution of CdCl2 and InCl3 at a substrate temperature of 300 °C. The structure, surface morphology, and the optoelectronic properties of prepared films were characterized respectively by means of X-ray diffraction (XRD), atomic force microscope and UV–visible spectroscopy. Based on the XRD results, the polycrystalline nature of CdO films has been confirmed, and In2O3 films were found to exhibit a preferred orientation along (222) diffracted plane. The grain size varies between 9.0 and 28.4 nm. The results of Hall effect measurement of CdO:In2O3 thin films confirms that all films were an n-type semiconductor. The electrical properties of prepared thin films and their sensitivity to nitrogen dioxide (NO2) gas are also studied. The influence of the operating temperature and In2O3 concentration on the NO2 response were investigated. It is found that all films are sensitive to NO2 gas, and the ideal operating temperature for the film contented 20 vol% of In2O3 was found to be 200 °C at a gas concentration of 25 ppm. The sensing mechanism of the CdO:In2O3 thin film is discussed and attributed to electron transfer between the sensing element and NO2 molecules.