Fabrication and characterization of transparent conductive ZnO:Al thin films prepared by direct current magnetron sputtering with highly conductive ZnO(ZnAl 2O 4) ceramic target

Abstract

Using a highly conductive ZnO(ZnAl 2O 4) ceramic target, c-axis-oriented transparent conductive ZnO:Al 2O 3 (ZAO) thin films were prepared on glass sheet substrates by direct current planar magnetron sputtering. The structural, electrical and optical properties of the films (deposited at different temperatures and annealed at 400°C in vacuum) were characterized with several techniques. The experimental results show that the electrical resistivity of films deposited at 320°C is 2.67×10 −4 Ω cm and can be further reduced to as low as 1.5×10 −4 Ω cm by annealing at 400°C for 2 h in a vacuum pressure of 10 −5 Torr. ZAO thin films deposited at room temperature have flaky crystallites with an average grain size of ∼100 nm; however those deposited at 320°C have tetrahedron grains with an average grain size of ∼150 nm. By increasing the deposition temperature or the post-deposition vacuum annealing, the carrier concentration of ZAO thin films increases, and the absorption edge in the transmission spectra shifts toward the shorter wavelength side (blue shift).