AVS 59th Annual International Symposium and Exhibition
    Energy Frontiers Focus Topic Thursday Sessions
       Session EN-ThP

Paper EN-ThP7
Texture-Etched Surface Structure Control of Transparent Conductive Impurity-Doped ZnO Films Deposited by r.f. Power Superimposed d.c. Magnetron Sputtering

Thursday, November 1, 2012, 6:00 pm, Room Central Hall

Session: Energy Frontiers Poster Session
Presenter: T. Minami, Kanazawa Institute of Technology, Japan
Authors: T. Minami, Kanazawa Institute of Technology, Japan
T. Fujita, Kanazawa Institute of Technology, Japan
T. Miyata, Kanazawa Institute of Technology, Japan
J. Nomoto, Kanazawa Institute of Technology, Japan
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This paper describes the influence of the supplied r.f. power on the light scattering characteristics and the surface texture formation obtainable by wet-chemical etching transparent conducting impurity-doped ZnO thin films prepared by an r.f. power superimposed d.c. magnetron sputtering deposition (rf+dc-MSD) using a high-density-sintered rectangular Al- or Ga--doped ZnO (AZO or GZO) target (127 mm×275 mm) : prepared with an Al2O3 content of 1 or 2 wt.% or Ga2O3 content of 5.7 wt.%, respectively. Both AZO and GZO thin films were prepared with a film thickness of either 1000 or 2000 nm on OA-10 glass substrates at a temperature of 200oC by varying both the supplied d.c. and r.f. power used in the rf+dc-MSD: d.c. power in the range of 0-800 W and r.f. power in the range of 0-1000 W. The surface texture formation was carried out by wet-chemical etching (in a 0.1% HCl solution at 25oC) conducted after heat-treatment with rapid thermal annealing (RTA) at 500 or 550oC for 5 min in air. It was found that the light scattering characteristics and surface texture formation obtainable for texture-etched AZO (or GZO) thin films were considerably dependent on both the ratio of supplied r.f. to d.c. power as well as the Al (or Ga) content doped into the films. In particular, the haze value was significantly improved at wavelengths up to about 1200 nm in the near-infrared region in surface-textured AZO films prepared with an increased ratio of supplied r.f. power to d.c. power and etched after being heat treated with RTA, whereas the film deposition rate was found to decrease with the increased power ratio. The obtained haze value improvement is attributable to an increase of etch pit size as well as a decrease of carrier concentration. In addition, the obtainable improvement in texture-etched AZO thin films was also found to be considerably dependent on the Al content doped into the films. In particular, texture-etched AZO thin films that are appropriate for transparent electrode applications in thin-film solar cells were obtained with the following preparation conditions: rf+dc-MSD using an AZO target with an Al2O3 content of 2 rather than 1 wt.%, r.f. power superimposed at an appropriate value and wet-chemical etching after heat-treatment with RTA. A high haze value above 80% at wavelengths up to 1100 nm in the near-infrared region was attained in texture-etched AZO thin films prepared by rf+dc-MSD (700 W r.f. component added to a constant d.c. power of 570 W) using an AZO target with an Al2O3 content of 2 wt.%.