Fast and broadband photoresponse in CdO thin film

Thermal annealing is recognized as an effective tool to manage the structural and electronic properties of oxide thin films. Combined with the atmospheric environment control, additional issues concerning surface effects act to change the performance of oxides for photodetectors purposes. The present investigation systematically studies morphological and optical properties and electrical transport of CdO thin films using an as-grown reference and annealed samples at 500 °C under O2 and N2 atmospheres. As-grown CdO presents fast and high photoresponses in a wide range of the visible spectrum, with an amplitude that reaches nearly 3000%. Also, a transition from negative to positive photoresistance was observed for temperatures below 230 K. From the analysis of the photoluminescence spectra, we noted two activation energies for as-grown CdO, whereas annealed samples presented only one. Therefore, the additional defect level, reduced after annealing, is responsible for the huge amplitude as well as the negative to positive transition in the photoresistance of as-grown CdO film. •Huge photoresponse amplitude of nearly 3000% is observed in CdO film.•A transition from negative to positive photoresponse is observed below 230 K.•Electrical resistance is reduced considerably under annealing.•Defect levels are responsible for the huge photoresponse and the observed transition.