Influence of thickness on optical and electrical properties of ZnO: Al thin films by DC-magnetron sputtered at room temperature

Without intentionally heating the substrates, polycrystalline aluminum doped zinc oxide (ZnO:Al, ZAO) thin films with good adhesion were prepared on glass substrates by DC magnetron sputtering. The structure and crystallization of the films were compared with the one deposited with substrate heating. The dependence of morphological, electrical and optical properties on film thickness was systematically investigated. The results showed that highly preferred (002) orientation ZAO film was produced at room temperature. The degree of crystallinity was improved, carrier concentration and mobility increased while the resistivity decreased with the film thickness growing. A "red-shift" was observed at the absorption edge, and the average transmittance in the visible and near-infrared range decreased with the increase of film thickness. ZAO film with a thickness of 1200 nm had the lowest sheet resistance of 6.1 Ω/□ and a resistivity of 7.315×10^-4 Ω·cm. Its average optical transmittance in visible range and the transmittance at 550nm was 82% and 87%, respectively.