Paper TF-TuP7
Influence of Doped Al Content on Electrical Properties and Light Management Obtainable by Texture-etched AZO Films Prepared by DC Magnetron Sputtering

Tuesday, November 1, 2011, 6:00 pm, Room East Exhibit Hall

Al-doped ZnO (AZO) thin films that would be suitable for transparent electrode applications in thin-film Si-based solar cells must necessarily attain not only a decrease of plasma resonance frequency by lowering the carrier concentration while retaining a resistivity on the order of 10^-4 Ωcm, but also a significant scattering of light incident on the film by surface texturing. In this paper, we describe the influence of doped Al impurity content on the electrical properties as well as the light management obtainable by surface texture-etched AZO thin films that were prepared with various Al contents by a dc magnetron sputtering (dc-MS) deposition and wet-chemically etched after a rapid thermal annealing (RTA) treatment. In addition, the stability of the resulting electrical properties for practical use in various environments was investigated for these AZO films prepared with various Al contents.

Transparent conducting AZO thin films were prepared with a thickness up to 2μm by a dc-MS deposition using sintered AZO targets that had various Al contents. The basic sputter depositions were carried out on OA-10 glass substrates at a temperature of 200^oC in a pure Ar gas atmosphere at a pressure of 0.4Pa and a power of 200W. Surface texturing of the AZO thin films was carried out by wet-chemical etching in a 0.1mol./l HCl solution after the thin films were heat treated with RTA at a temperature of 300-500^oC for 1-5min in air. It was found that the obtainable surface texture and electrical properties in texture-etched AZO thin films were considerably affected by the RTA treatment conditions as well as the Al content doped into the films. The transmittance in the near-infrared region of the resulting AZO thin films exhibited a tendency to improve as the RTA temperature was increased. A high transmittance above 80% at a wavelength of 1.2μm was obtained in 1-μm-thick-AZO thin films prepared under the following conditions: an Al content (Al/(Al+Zn) atomic ratio) of approximately 0.5at.% when the thin films were heat treated without RTA and an Al content below 1.5at.% when the thin films were heat treated with RTA. In addition, when the thin films were heat treated with RTA at 500^oC for 3-5min, increasing the Al content doped into the AZO films enhanced the transmittance in the near infrared region , irrespective of the film thickness. However, it should be noted that the optimal Al content doped into texture-etched AZO thin films that would be suitable for transparent electrode applications in thin-film Si-based solar cells was considerably dependent on the obtainable crystallinity in the films as well as whether the thin films were heat treated with RTA or not.