Thickness Dependent Room Temperature Sensing Properties of Spray Pyrolysis Deposited Nanostructured ZnO Thin Films

Zinc oxide (ZnO) thin films were deposited on glass substrates using spray pyrolysis technique at various substrate temperatures such as 523 K, 623 K and 723 K. Zinc nitrate hexahydrate was used as precursor salt. Structural studies revealed that all the films were preferably oriented towards (0 0 2) crystal plane. Depending on the substrate temperature, the intensity of the (0 0 2) plane was found to be varied. Uniformly distributed spherical nano-grains were formed in all the deposited films and their size was increased with respect to increased substrate temperature. Optical band gap was found to be 3.15, 3.12 and 3.19 eV for films deposited at 523 K, 623 K and 723 K respectively. Thickness of the films was modulated by varying the substrate temperature. The influence of film thickness on the room temperature sensing characteristics of ZnO thin films was investigated. The film with lower thickness showed better response towards acetaldehyde vapour and the lowest detection limit (LDL) was found to be 5 ppm.