Elsevier

Materials Research Bulletin

Volume 47, Issue 10, October 2012, Pages 2895-2897
Materials Research Bulletin

Effects of intermediate metal layer on the properties of Ga–Al doped ZnO/metal/Ga–Al doped ZnO multilayers deposited on polymer substrate

https://doi.org/10.1016/j.materresbull.2012.04.104Get rights and content

Abstract

Ga–Al doped ZnO/metal/Ga–Al doped ZnO multilayer films were deposited on polyethersulfone (PES) substrate at room temperature. The multilayer films consisted of intermediate Ag metal layers, top and bottom Ga–Al doped ZnO layer. The multilayer with PES substrate had advantages such as low sheet resistance, high optical transmittance in visible range and stable mechanical properties. From the results, sheet resistances of multilayer showed 9 Ω/sq with 12 nm of Ag metal layer thickness. Average optical transmittance of multilayer film showed 84% in visible range (380–770 nm) with 12 nm of Ag metal layer thickness. Moreover the multilayers showed stable mechanical properties than single-layered Ga–Al doped ZnO sample during the bending test due to the existence of ductile Ag metal layer.

Introduction

Zinc oxide (ZnO) thin film have been used for applications in many fields, such as thin film solar cells, liquid crystal display, organic light emitting diode and plasma display panels [1], [2], [3]. The ZnO thin film has advantages, such as low cost, stability in hydrogen plasma, non-toxicity and high transmittance in the visible range [4]. The ZnO is n-type semiconductor with the wide direct band gap of 3.37 eV and large exciton binding energy of 60 meV [5]. Doped ZnO, such as Al doped ZnO (AZO) [6], Ga-doped ZnO (GZO) [7], indium doped ZnO (IZO) [8], indium zinc tin oxide (IZTO) [9], Zr-doped ZnO (ZZO) [10], Mo-doped ZnO (MZO) [11], and co-doped Ga–Al doped ZnO [12], [13] have been widely investigated due to their excellent properties. However, the resistivity of these doped ZnO is not low enough in some cases for improved applications [14]. In order to enhance the conductivity of transparent conducting films, it is necessary to try new materials. It is well known that the conductivity of metal films is very high, but their optical transmittance in visible range is relatively low [15]. Fan et al. [16] reported that the dielectric/metal/dielectric multilayer film could suppress the reflection from the metal in the visible region and achieve a selective transparent effect. Recently, a multilayer structure, such as TCO/metal/TCO, has been proposed use in transparent conducting materials. Moreover, the multilayers exhibits stable mechanical properties than single-layered TCO sample during the bending test due to the existence of ductile metal layer. In this work, we investigate Ga–Al doped ZnO/metal(Ag)/Ga–Al doped ZnO multilayer as a function of thickness of intermediate Ag metal layer grew on PES substrate using the facing targets sputtering (FTS) system.

Section snippets

Experimental

The FTS system was designed to array the two targets to face each other and so form high density plasma between the targets. The FTS system was able to restrain the bombardment of the substrate by high-energy particles because the substrate's position was located outside of the plasma. Consequently, the FTS system suppresses the substrate damage caused by high-energy particles, such as electrons and partial ions [6], [17]. In this work, the Ag targets were installed on top and the GZO (ZnO:Ga2O3

Results and discussion

Fig. 1, Fig. 2 show the sheet resistance and optical transmittance in visible range of multilayer as a function of intermediate Ag metal layer. Increased thickness of Ag metal layer from 6 nm to 9 nm, the sheet resistance sharply decreased. The sheet resistance of multilayer showed 510, 216, 71, 18, 9, 6 and 5 Ω/sq with 0 (single-layered Ga–Al ZnO), 3, 6, 9, 12, 15 and 18 nm thicknesses, respectively. The sheet resistance depended on the thickness of intermediate Ag metal layer, because the Ag

Conclusions

In this work, electrical, structural, optical and mechanical properties of Ga–Al doped ZnO/metal(Ag)/Ga–Al doped ZnO multilayer structure on PES substrate investigated as a function of Ag thickness. As 12 nm of Ag metal layer thickness, sheet resistance and average optical transmittance in visible range of multilayer thin film 9 Ω/sq and 84%, and figure of merits exhibited 1.94 × 10−2 Ω−1. Moreover the multilayers showed stable mechanical properties than single-layered Ga–Al doped ZnO sample during

Acknowledgments

This work was supported by Gachon University Research Fund 2012 and the Human Resources Development of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Knowledge Economy (No. 20104010100510).

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