Transparent Conductive Oxide Semiconductor ZnO:Al Films Produced by Magnetron Reactive Sputtering
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Transparent Conductive Oxide Semiconductor ZnO:Al Films Produced by Magnetron Reactive Sputtering CHEN Meng1,2, PEI Zhiliang2, Wang Xi1, SUN Cao2, WEN Lishi2 1 (Ion Beam Laboratory, Shanghai Institute of Metallurgy, Chinese Academy of Sciences, Shanghai, China, 200050, E_mail: [email protected]) 2 (Institute of Metal Research, Chinese Academy of Sciences, Shenyang, China, 110015) ABSTRACT ZnO:Al (ZAO) films were deposited on quartz substrates by dc magnetron reactive sputtering from a Zn target mixed with Al. The effect of substrate temperature and Al doping content on the structural, electrical and optical properties of ZAO films were investigated. It was observed that the (002) peak position of all films shifts to lower angle comparable to that of bulk ZnO due to the residual stress change with deposition parameters. The dependences of electrical properties such as resistivity, carrier concentration and Hall mobility on substrate temperature and Al doping content were measured. The minimum resistivity is 4.23×10-4 Ω.cm with the carrier concentration of 9.21×1020 cm-3 and Hall mobility of 16.0 cm2v-1s-1. The visible transmittance of above 80% was obtained. The optical band gap was observed to increase with increasing carrier concentration. The possible mechanisms are discussed. INTRODUCTION The greatly increasing use of transparent conducting films for solid-state display devices especially in flat panel display devices has promoted the development of inexpensive materials such as ZnO and tin oxide (SnO2), in place of indium tin oxide (ITO). Among them, Al-doped ZnO (ZAO) films show good electrical and optical properties and are emerging as a potential alternative candidate for ITO films. Furthermore, they offer a number of advantages compared to the predominant ITO films nowadays [1,2]: (i) cheap and abundant raw materials; (ii) nontoxicity; (iii) tailoring of the ultraviolet absorption because the fundamental band gap of ZnO lies just at the end of the luminous spectrum; (iv) good stability in hydrogen plasma, which is of significance for applications related to amorphous silicon solar cells, etc. Most researchers have focused on oxide targets, and the properties of the resulting ZAO films have been greatly improved. The drawback of using an oxide target is its low deposition. However, using targets of Zn-Al alloys attracting great interest in reactive sputtering because of their desirable features including: a) higher deposition rate; b) easier fabrication of the alloy target and c) accurate control of the film thickness. In reactive sputtering deposition of ZAO films, the properties of ZAO films are strongly influenced by deposition parameters such as the Al content in the target, substrate temperature (Ts), ambient gas and pressure (Pw) and discharge power. Therefore, it is meaningful to study the effects of the deposition parameters in order to obtain ZAO films with optimum properties. In this article, we report on structural, electrical and optical properties of the films prepared by magnetron reactive s
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