Comparative Analysis of Highly Sensitive Ammonia Gas Sensors Based on ZnO, CdO, and CdZnO Thin Films

CdO, ZnO, and CdZnO thin films were deposited using the nebulizer spray pyrolysis method, and their properties were investigated for gas sensing applications. The deposition process involved the use of analytical reagent-grade chemicals and a nebulizer spray pyrolysis setup. X-ray diffraction analysis revealed the cubic and hexagonal crystal structures of the films, with distinct peak positions corresponding to CdO and ZnO. The addition of CdO influenced the growth kinetics and crystallization behavior of the films, leading to an increase in the average crystallite size of CdZnO films compared to pure ZnO films. Optical analysis showed that CdO, CdZnO, and ZnO films had direct band gaps of 2.3 eV, 3.03 eV, and 3.18 eV, respectively. The gas sensing properties of CdO films were investigated, and the sensing mechanism was elucidated in terms of electron release and capture by chemisorbed oxygen species. Impedance spectroscopy measurements demonstrated the sensitivity of the CdO sensor to different concentrations of ammonia gas. The fabricated CdO sensor exhibited enhanced sensitivity at room temperature compared to higher temperatures. Overall, the CdO, ZnO, and CdZnO thin films show promise for gas sensing applications.