Light intensity effects on the sensitivity of ZnO:Cr gas sensor

Chromium-doped zinc oxide thin films (Cr: ZnO) with different Cr concentration were prepared using a homemade nebuliser spray pyrolysis system, and the influence of Cr doping level on the physical properties and the influence of light on the gas-sensing properties of ZnO films were investigated. The XRD results reveal that the hexagonal wurtzite structure of ZnO was not affected by the Cr doping. All the films have average transmittance about 85% in the visible region. The film shows good sensing behaviour against ammonia gas under dark condition than ambient (64lx) and 150W (5840lx) incandescent lights. Of the tested samples, ZnO:Cr film with 2at.-% of Cr doping shows the best response and recovery time for ammonia gas. The reasons for the enhanced sensing ability of the doped films were explained with the help of FESEM, AFM and optical results.