Effect of discharge power density on the properties of Al and F co-doped ZnO thin films prepared at room temperature

ZnO transparent conducting thin films co-doped with aluminium and fluorine (AZO:F) were prepared on glass substrates by RF magnetron sputtering at room temperature. The effect of discharge power density on the microstructure, surface morphology, electrical and optical properties was investigated. From XRD analysis, it was revealed that the intensity of (002) favoured orientation of ZnO films increased with power density from 2.6 to 6.1 W/cm2 and then turned to a randomly orientated structure as power density continuously increased to 7.8 W/cm2. The film prepared at 6.1 W/cm2 showed a better crystallization and microstructure with larger, pyramid-like grains that were approximately 180 nm long and 90 nm wide. As a result, the electrical resistivity of the AZO:F films had a minimum of 4.1 × 10−4 Ωcm. The improvement in the electrical resistivity of AZO:F films was due to the increase in carrier concentration from 8.8 × 1020 to 1.38 × 1021 cm−3 and the mobility from 5.8 to 11.8 cm2 V−1 s−1. The increase in carrier concentration with power density was also found to affect the optical property of the films due to the Moss-Burstein shift.