Phase formation, growth kinetics and optical properties of 0.5ZnO-0.5CdO thin films synthesized by sol-gel spin coating processes

The phase formation, growth kinetics and optical properties of 0.5ZnO-0.5CdO thin films have been investigated by X-ray diffraction (XRD) and UV–vis spectrophotometry. The XRD results show that all 0.5ZnO-0.5CdO thin films are composed of CdO as the major phase and ZnO as the secondary phase. Moreover, after annealing of the 0.5ZnO-0.5CdO thin films at 723   K for 45   min and 773   K for 30   min, the minor phase of CdSiO 3 also appeared. The average activation energy of CdO grain growth in 0.5ZnO-0.5CdO thin films by the isothermal method is 10.51±1.17   kJ/mol. The average optical transparency was nearly 80% for the wavelength range from 500   nm to 900   nm. The grain size of CdO on the band gap energy for 0.5ZnO-0.5CdO thin films after annealing has a critical value, namely 15.9   nm. When the grain size of CdO is smaller than 15.9   nm, the band gap energy decreases, showing a redshift effect. Conversely, the band gap energy increases when the grain size of CdO is greater than 15.9   nm, showing a blueshift effect.