Structural, optical, electrical and gas sensor properties of Fe-doped CdO thin films synthesized by spray pyrolsis

In this study, the structural, optical, electrical and gas sensor properties of Fe-doped CdO thin films synthesized using the spray pyrolysis method were investigated as a function of Fe doping. The characterizations of the thin films were made by using X-ray diffraction (XRD), X-ray photoelectron (XPS), ultraviolet–visible (UV-VIS), field emission-scanning electron microscope (FE-SEM), atomic force microscope (AFM) and Hall measurements. In addition, the response values of the films for H2 gas were determined by a current-sensitive gas sensor measurement system. XRD analyzes revealed that the produced films were in polycrystalline cubic structure and their unit cell volumes were reduced by Fe doping. The mean particle size and mean dislocation density of Fe doped samples were obtained as 11.99 nm and 6.98 × 1015 (line/m2), respectively. XPS results showed that the experimentally obtained doping ratios of the produced films were very close to the planned doping ratios and the formation of CdxFe(1-x)-O2 and CdxFe(1-x)-O3 on the surfaces of the samples decreased with the increment of Fe doping. UV-VIS measurements demostrated that the band gap is generally reduced due to doping, in line with the Moss-Burstein effect. According to Hall results, the mobility of the samples increases with increasing doping. SEM and AFM analyzes revealed that Fe doping to CdO causes nanoroads formation on thin film surfaces, and nanoroads disappear in 4 % and 5 % doped films. In addition to the specified characterizations, how these changes in the surface morphology of the films with Fe doping affect the H2 gas responses of the samples is also explained in the study.