Effect of annealing and room temperature sputtering power on optoelectronic properties of pure and Al-doped ZnO thin films

Transparent ZnO and Al-doped ZnO (AZO) thin films have been prepared by radio frequency sputtering deposition at room temperature. The optical, electrical, and structural characteristics of the obtained films have been extensively investigated as a function of sputtering and annealing parameters. Spectrophotometry, X-ray diffraction (XRD), atomic force microscopy (AFM), four-point probe and Hall-effect measurements were employed. The ZnO films generally exhibited excellent crystalline properties, while providing a UV cut-off in the absorption spectrum for optical filtration. AZO thin films exhibited an average transparency (larger than 85%) over the visible region of the spectrum, and resistivity of the order of 10−3 Ω cm was obtained. The carrier concentration and electron mobility values proved to be dependent on the deposition parameters and annealing temperature. The obtained results showed that annealing temperatures higher than 400 °C were not necessary and potentially degraded the electronic properties of the AZO thin films.