Microstructure and optical properties of ZnO:Al films prepared by radio frequency reactive magnetron sputtering

Pure and Al-doped ZnO (ZnO:Al) films have been deposited using radio frequency (RF) reactive magnetron sputtering at the O2:Ar ratio of 10:10, 6:10, and 2:10 sccm and 150 °C. The substrate temperatures were room temperature (RT), 150, 250, and 350 °C and the O2:Ar ratio was 6:10 sccm during the magnetron sputtering. The microstructures and optical properties in doped ZnO films were systematically investigated by X-ray diffraction (XRD) and fluorescence spectrophotometry. The results indicate that ZnO:Al films prepared at 250 °C and 6:10 sccm had the best crystal quality among all ZnO:Al films. Photoluminescence (PL) measurements at room temperature reveal a green and two blue emissions. The origin of these emissions is discussed. In addition, the intensity of blue emission peak first increased and then decreased as the substrate temperature shifted from RT to 350 °C. The most intense blue luminescence was obtained from a sample grown at the O2:Ar ratio of 6:10 sccm and 150 °C.