The effect of Cu on the properties of CdO/Cu/CdO multilayer films for transparent conductive electrode applications
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The effect of Cu on the properties of CdO/Cu/CdO multilayer films for transparent conductive electrode applications M. Raaif1 • S. H. Mohamed1
Received: 28 September 2016 / Accepted: 18 May 2017 / Published online: 26 May 2017 Springer-Verlag Berlin Heidelberg 2017
Abstract Transparent conductive CdO/Cu/CdO multilayer films were prepared using rf plasma magnetron sputtering and electron beam evaporation techniques. The CdO layers were prepared using rf plasma magnetron sputtering, while the Cu interlayer was prepared by electron beam evaporation technique. The Cu layer thickness was varied between 1 and 10 nm. The structural and optical properties as well as the sheet resistance of the multilayer films were studied. X-ray diffraction measurements revealed the presence of cubic CdO structure and the Cu peak was only observed for the multilayers prepared with 10 nm of Cu. It has been observed that the Cu interlayer thickness has a great influence on the optical and electrical properties of the multilayers. The transmittance of the multilayer films decreased while the reflectance increased with increasing Cu interlayer thickness. The refractive index and the extinction coefficient of the multilayer films were calculated. The estimated optical band gap values were found to be decreased from 2.75 ± 0.02 to 2.40 ± 0.02 eV as the Cu interlayer thickness increased from 1 to 10 nm. The sheet resistance was sensitive to the Cu interlayer thickness and it decreased with increasing Cu interlayer thickness. A sheet resistSSance of 21.7 X/sq, an average transmittance (between 700 and 1000 nm) of 77%, and an optical band gap of 2.5 ± 0.02 eV were estimated for the multilayer film with 2 nm Cu layer. The multilayer film with 2 nm Cu layer has the highest figure of merit value of 3.2 9 10-3 X-1. This indicates that the properties of this
& S. H. Mohamed [email protected] 1
Physics Department, Faculty of Science, Sohag University, Sohag 82524, Egypt
multilayer film are suitable for transparent conductive electrode applications.
1 Introduction Thin films of transparent conducting oxides (TCOs) have many optical and electrical applications such as solar cells, optoelectronics, gas sensors, flat panel displays, touchscreens, organic light-emitting diodes and thin film resistor displays [1–3]. Multilayer films of MOx/metal/MOx (where MOx represents metal oxides) have emerged recently as superior TCOs [4–10]. The multilayers for practical use are ZnO/Cu/ZnO [4], ZnO/Ag/ZnO [5], TiOx/Ag/TiOx [6], ITO/Cu/ITO [7], SnO2/Cu/SnO2 [8], SnO2/Ag/SnO2 [9] and WO3/Ag/WO3 [10]. Various advantages have been found for these multilayers in comparison with the single layer: (i) the optoelectronic properties of the multilayers are enhanced without heating or post-annealing the structure of the films, (ii) much lower resistivity for the multilayer is obtained in comparison with the single-layer films of the same thickness and (ii) lower oxide film thickness can be used as the conductivity is controlled by the metal layer thickness [5, 7]. The metal
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