Dependence of Ga-doped ZnO thin film properties on different sputtering process parameters: Substrate temperature, sputtering pressure and bias voltage

• Published in: Thin solid films 2015-07, Vol.586, p.13-21
• Main Authors: Castro, M.V., Tavares, C.J.
• Format: Article
• Language: English
• Subjects: Bias; Bias voltage; Deposition; Electric potential; Electrical properties; Gallium-doped zinc oxide; Pressure; Process parameters; Sputtering; Substrate temperature; Thin films; Transparent conducting oxide; Voltage; Zinc oxide
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2015.04.036

This paper reports on the effects of different sputtering deposition process parameters (substrate temperature, sputtering pressure and bias voltage) on the electrical, optical, structural and morphological properties of gallium-doped ZnO (ZnO:Ga) of ~1μm thick. These highly transparent and conductive films were deposited on glass surfaces by d.c. pulsed magnetron sputtering from a GZO (ZnO(95.5):Ga2O3(4.5)) ceramic target in an argon atmosphere. X-ray diffraction experiments show that all films have a hexagonal wurtzite structure with the [001] preferred crystallographic direction, and the morphology of the films (obtained from scanning electron microscope analysis) is sensitive to the process parameters. All ZnO:Ga films have an average transmittance above 80% in the visible region, and the lowest electrical resistivity of 3.03×10−4Ω·cm was achieved for the sample submitted to the lowest bias voltage (−40V), which corresponds to a carrier concentration and a carrier mobility of 6.99×1020cm−3 and 29.49cm2V−1s−1, respectively. A high substrate temperature, high sputtering pressure and low negative bias voltage (within the range of studied parameters) proved to be very promising on obtaining optimized ZnO:Ga films, ensuring suitable properties for application as transparent electrodes in photovoltaic cells. •Synthesis of ZnO:Ga thin films by d.c. pulsed magnetron sputtering•High transparency and electrically conductive ZnO:Ga thin films•Effect of sputtering process parameters on microstructure, electrical and optical properties