Structural and optical properties of Al/ZnO thin films deposited by radio frequency sputtering

The effects of annealing temperature and variation of sample thickness on the structural and optical properties of zinc oxide thin films with aluminium contact (Al/ZnO) have been investigated. The study involved the synthesis of a bilayer thin film of Al/ZnO with varied thicknesses on a glass slide substrate by using radio frequency magnetron sputtering deposition technique. 99.99% pure ZnO and aluminium were used as the sputtering target. The films were then annealed in vacuum at annealing temperatures of 200 °C and 400 °C. The structural and optical properties of Al/ZnO thin films grown were characterized by x-ray diffraction (XRD) and optical measurements respectively. The results obtained from the XRD patterns showed that Al/ZnO films (both as-deposited and annealed), exhibits a crystalline structure with (002) preferred orientation. The peak intensity of the preferred plane increases as the annealing temperature increases. The optical studies of the Al/ZnO films showed a maximum value of transmittance ranging from 82% to 91% depending on the condition of the films. A decrease in transmittance as the thickness of the films increases was observed. The transmittance also increased with increasing annealing temperature. The energy gaps ( E _g) were determined from the transmittance data and found to be in the range 3.73–3.83 eV. The results obtained from the experiment also show that the optical band gap increases as the thickness and annealing temperature increase. (paper)