Influence of annealing temperature on the photoelectric gas sensing of Fe-doped ZnO under visible light irradiation

Fe-doped ZnO are fabricated by hydrothermal method. The influence of the annealing temperature on structural and photoelectric property was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–vis diffuse reflectance spectra (UV–vis DRS). Visible light-illumination room-temperature gas sensing to formaldehyde based on Fe-doped ZnO annealed at different temperatures was subsequently investigated by the surface photocurrent spectra and gas sensor characterization system, respectively. Accompanying with increasing annealing temperature from 400 °C to 600 °C, the response to formaldehyde was enhanced due to the increase in crystal quality and active sites on the surface of Fe-doped ZnO. However, when the annealing temperature goes over 700 °C, the phase of ZnFe2O4 was observed from XRD pattern. The existence of ZnFe2O4 hindered the transfer of photo-generated carriers and decreased the amount of surface active sites. As a result, the photoelectric gas response for formaldehyde was weaken to some extent. Our results demonstrated that annealing temperature is a very important parameter in the determination of the sensitivity of photoelectric gas sensing based on Fe-doped ZnO.