Nanocomposite Co(3)O(4)-ZnO Thin Films for Photoconductivity Sensors

Thin nanocomposite films based on zinc oxide (ZnO) added with cobalt oxide (Co(3)O(4)) were synthesized by solid-phase pyrolysis. According to XRD, the films consist of a ZnO wurtzite phase and a cubic structure of Co(3)O(4) spinel. The crystallite sizes in the films increased from 18 nm to 24 nm with growing annealing temperature and Co(3)O(4) concentration. Optical and X-ray photoelectron spectroscopy data revealed that enhancing the Co(3)O(4) concentration leads to a change in the optical absorption spectrum and the appearance of allowed transitions in the material. Electrophysical measurements showed that Co(3)O(4)-ZnO films have a resistivity up to 3 × 10(4) Ohm∙cm and a semiconductor conductivity close to intrinsic. With advancing the Co(3)O(4) concentration, the mobility of the charge carriers was found to increase by almost four times. The photosensors based on the 10Co-90Zn film exhibited a maximum normalized photoresponse when exposed to radiation with wavelengths of 400 nm and 660 nm. It was found that the same film has a minimum response time of ca. 26.2 ms upon exposure to radiation of 660 nm wavelength. The photosensors based on the 3Co-97Zn film have a minimum response time of ca. 58.3 ms versus the radiation of 400 nm wavelength. Thus, the Co(3)O(4) content was found to be an effective impurity to tune the photosensitivity of radiation sensors based on Co(3)O(4)-ZnO films in the wavelength range of 400–660 nm.