Comparative material study on RF and DC magnetron sputtered ZnO:Al films

ZnO:Al films were prepared on glass substrates by RF and DC sputtering from ceramic ZnO:Al2O3 targets. The film properties of RF sputtered ZnO:Al showed a weak dependence on film thickness and substrate temperature while a strong dependence on sputter pressure and oxygen addition to the process gas was observed. For DC sputtering in static mode at 270 °C a low resistivity of 2.3–5 × 10− 4 Ω cm was obtained in a wide pressure range of 0.04 to 4 Pa. At lower substrate temperatures the supply of small amounts of oxygen was required to maintain high transparency and achieve significant roughness for light scattering after wet chemical etching. Highest damp heat stability was found for ZnO:Al films deposited at low sputter pressures. This behavior could be correlated to the highly compact film structure of these films. ZnO:Al films deposited in dynamic DC mode exhibited inferior resistivity of 8–40 × 10− 4 Ω cm, which partly could be attributed to the specific design of the inline sputter system.