Effects of Al content on the properties of ZnO:Al films prepared by Al2O3 and ZnO co-sputtering

Abstract

Aluminum doped zinc oxide (AZO) films were deposited on quartz substrates by radio-frequency magnetron co-sputtering method with ZnO and Al2O3 ceramic targets. The structural, optical and electrical properties of these films as a function of the Al content were investigated. XRD results reveal that the AZO films are wurtzite structure with (002) preferred orientation. The average transmittance of all the films is higher than 80% in a wide wavelength range from 400 to 1,500 nm. The band gap energy, calculated from their optical absorption spectra, is in the range of 3.50–3.66 eV depending on the Al content. Doping of Al3+ in the ZnO makes the film surface roughness decrease. The dopant Al3+ acts as electron donor by which the electrical conductivity and carrier concentration of the films are obviously increased until the Al3+ reaches its saturation content of about 4.50 at.%.