Effect of In incorporation on the structural, electrical, and gas sensing properties of ZnO films

In this paper, we report some comparative results on the structural, electrical, and gas sensing properties of undoped, In-doped ZnO, and ZnO-In2O3 thin films, respectively. The oxide films were obtained by thermal oxidation (flash oxidation) of metallic films, deposited by thermal evaporation under vacuum. X-ray diffraction patterns reveal that oxidized films are polycrystalline, the crystallites being preferentially oriented with (002) planes parallel with the substrate. It was observed that the films' morphology, investigated by atomic force microscopy and scanning electron microscopy, is influenced by the In amount. The temperature dependence of electrical conductivity was studied and obtained results indicate that In-doped ZnO and ZnO-In2O3 films exhibit an enhancement of electrical conductivity with four orders of magnitude by comparison with undoped ZnO film. Gas sensitivity measurements were performed for four different gases (ammonia, methane, acetone, and ethanol), and it was observed that all investigated films are more sensitive to ammonia. Also, it was observed that gas sensitivity is visibly increased for In-doped ZnO and ZnO-In2O3 samples by comparison with undoped ZnO film.