Structural and Optical Properties of Cu Doped ZnO Thin Films by Co-Sputtering

This paper reports on the structural and optical properties of ZnCuO thin films that were prepared by co-sputtering for the application of p-type-channel transparent thin-film transistors (TFTs). Pure ceramic ZnO and metal Cu targets were prepared for the co-sputtering of the ZnCuO thin films. The effects of the Cu concentration on the structural, optical, and electrical properties of the ZnCuO films were investigated after their heat treatment. It was observed from the XRD measurements that the ZnCuO films with a Cu concentration of 7% had ZnO(002), Cu₂O(111), and Cu₂O(200) planes. The 7% Cu-doped ZnO films also showed a band-gap energy of ∼2.05 eV, an average transmittance of ∼62%, and a p-type carrier density of ∼1.33 × 10¹⁹ cm⁻³ at room temperature. The bottom-gated TFTs that were fabricated with the ZnCuO thin film as a p-type channel exhibited an on-off ratio of ∼6. These results indicate the possibility of applying ZnCuO thin films with variable band-gap energies to ZnO-based optoelectronic devices.