A study on structural formation and optical properties of Zn1-xCdxO thin films synthesized by the DC and RF reactive magnetron co-sputtering

The Zn1-xCdxO thin films were prepared on quartz by the direct current (DC) and radio frequency (RF) reactive magnetron co-sputtering technique with Zn and Cd metal targets. The influence of RF power on Cd target (PCd) on the structure and optical properties of Zn1-xCdxO films was investigated by using X-ray diffraction (XRD), transmission electron microscope (TEM), optical absorbance and photoluminescence (PL) measurements. The concentration and chemical states of Cd in films have been confirmed by energy dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS) analysis. The results indicated that as the PCd varied from 0 to 120 W, all the Zn1-xCdxO thin films had a hexagonal wurtzite structure of pure ZnO and highly (002) preferred orientation, the Cd relative content in film is increased and the Zn relative content is decreased. Correspondingly, the optical band-gap of Zn1-xCdxO thin films with hexagonal wurtzite structure are tuned from 3.24 (PCd = 0) to 2.82 eV (PCd = 120 W). The location of the near-band-edge (NBE) emission peaks shift toward lower energy side from 388 to 440 nm, which is attributed to the decrease of band gap caused by Cd substitution.