Structural, optical and electrical properties of transparent conducting CuInO 2 thin films prepared by RF sputtering
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Structural, optical and electrical properties of transparent conducting CuInO2 thin films prepared by RF sputtering
Bin Yang, Yunbin He, Angalika Polity and Bruno K. Meyer I. Physikalisches Institut, Justus - Liebig - Universität Giessen, Heinrich-Buff-Ring 16, D - 35392 Giessen, Germany
ABSTRACT The transparent conducting CuInO2 thin films were prepared by radio frequency (RF) reactive sputtering and post growth annealing. A study of structural, optical, and electrical properties was performed on the films. The crystalline phase in the films was identified to be the delafossite structure. The optical properties, such as the wavelength dependence of the transmittance and the band gap energy, were determined. The average transmittance is 70% in the wavelength range of 400-1100 nm and the band gap is ≈ 3.7 eV. The temperaturedependence of electrical conductivity in the CuInO2 delafossite thin films was measured from 70 to 400K. The resistivity, carrier density, and mobility of the thin films at 300K were 1.8×101 Ωcm, 1.6×1019 cm-3 and 2×10-1 cm2/Vs, respectively. Hall coefficient indicated that the CuInO2 thin films are n-type conductors. The electrical conductivity showed semiconducting type at room temperature.
INTRODUCTION In recent years, transparent conducting oxide compounds with the delafossite structure have attracted much attention because of their potential in preparing novel transparent p-n junction for device applications such as functional windows and ultraviolet light-emitting diodes [1-3]. Various research groups are working on different kinds of materials like ZnO, In1-xSnxO3, CuAlO2 and SrCuO2 etc. for synthesis of transparent conducting oxide thin films and also on device preparation using them [3-6]. Recently, the delafossite oxide of CuInO2 showed bipolar conductivity with different doping ions. Yanagi et al. reported the preparation of two kinds of CuInO2 thin films by pulsed laser deposition technique, where substitution of In3+ with Ca2+ and Sn4+ result in p-type and n-type conduction, respectively[7]. For the preparation of CuInO2 thin films, most of the research groups used pulsed laser deposition (PLD) with a bulk CuInO2 target. Unfortunately, PLD is not a technique employed by industries. There are some limitations of this method such as the difficulty in scaling-up of the technology and the low quality films due to the droplet formation. Hence, it is of utmost to develop alternative fabrication route for the full exploitation of its technological potential. Reactive sputtering, a commonly used thin film deposition technique in industrial wafer preparation, would be more suitable for mass production because large-area deposition is possible by this method. In this work, transparent conducting CuInO2 thin films have been deposited on quartz substrates by RF sputtering using a Cu-In alloy target in a mole ratio of 11:9 (Cu : In). We preferred the Cu-In alloy target over CuInO2 ceramic target because it is much more convenient
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to prepare Cu-In alloy than CuInO2 ceramic. A
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