Tailoring Electrical Conductivity and Mechanism of Carrier Transport in Zinc Oxide with Embedded Ag Layer
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1074-I05-15
Tailoring Electrical Conductivity and Mechanism of Carrier Transport in Zinc Oxide with Embedded Ag Layer Hauk Han1, N D Theodore2, and Terry Alford1 1
School of Materials and Flexible Display Center at ASU, Arizona State University, Tempe, AZ, 85287 2
Freescale Semiconductor Inc, Tempe, AZ, 85284
ABSTRACT The effects of an embedded silver layer on the electrical properties of zinc oxide (ZnO) / silver (Ag)/ zinc oxide (ZnO) layered composite structures on polymer substrates have been investigated. We have engineered transparent conducting oxide structures with greatly improved conductivity. Electrical properties are correlated with Ag thickness. Film thicknesses were determined using Rutherford backscattering spectrometry. Hall effect, 4-point probe, and UV-Vis spectrophotometer analyses were used to characterize electrical and optical properties. The results show that carrier concentration, mobility, and conductivity increase with Ag thickness. Increasing Ag thickness from 8 to 14 nm enhances sheet resistance and resistivity by six orders of magnitude. We describe of the influence of Ag thickness on electrical properties of the ZnO/Ag/ZnO composite and propose a conduction mechanism for this system. INTRODUTION Transparent conducting oxides (TCOs) are used for solar cells and other opto-electronic applications, where transparent electrodes are used to convey electric signals. The TCO materials are useful due to their unique combination of electro-optical properties (high visible transparency and high electrical conductivity) [1]. In order to obtain higher energy conversion efficiencies in solar cells as well as higher speed and energy efficiency of opto-electronic devices, transparent electrodes must have high electrical conductivity combined with high transmittance. TCO-metal-TCO multilayer systems have been tried and studied for improving the conductivity [2,3]. These systems have very low sheet resistance, comparable optical transparency in the visible range, lower thickness than single-layered TCO films, and better durability than single-layered metal films. Various studies have documented the electrical and optical properties of ITO and ZnO multilayers with silver (Ag) (ITO/Ag/ITO and ZnO/Ag/ZnO) [2,3]. However the detailed mechanism of electrical transport in these systems is still not clear. In this study, a structure consisting of two outer layers of ZnO and a middle-layer of Ag was prepared to enhance the overall electrical conductivity and to investigate how the Ag layer
affects electrical transport and optical properties when deposited on flexible substrates. EXPERIMENT DETAILS ZnO/Ag/ZnO thin films were deposited on PET polymer substrates by RF sputtering of ZnO and DC sputtering of Ag at room temperature. Sputtering was performed using ZnO and metal Ag sputter targets. The base pressure before deposition was approximately 1 × 10-7 Torr. Sputtering was carried out at a pressure of 10 mTorr in pure Ar. The thickness of the ZnO outer layer was fixed at 35 nm and Ag layers were varied be
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