Control of the Formation of Zn 1-x Mg x O Films by Zinc Sulfate Concentration
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Control of the Formation of Zn1-xMgxO Films by Zinc Sulfate Concentration Hiroki Ishizaki1 and Seishiro Ito2 Department of Electronic System Engineering, Tokyo University of Science Suwa, 5000-1 Toyohira, Chino-shi, Nagano 391-0292, Japan 2 Faculty of Science and Engineering, Kinki University, 4-1 Kowakae 3-chome, Higashiosaka, Osaka 577-8502, Japan 1
ABSTRACT Magnesium doped ZnO films were electrochemically grown on the NESA conductive glass substrate from the magnesium nitrate aqueous solution with zinc sulfate, kept at 323K and the cathodic potential of -0.9V vs. Ag/AgCl. The Mg/(Mg+Zn) atomic ratio of Zn1-xMgxO films increased with the decrease in the zinc sulfate concentration. The optical band gap energy of these Zn1-xMgxO films decreased with increasing content of zinc sulfate. Thus, the optical band gap energy and Mg/(Mg+Zn) atomic ratio of Zn1-xMgxO films would depend on the zinc sulfate concentration. INTRODUCTION Recently, Zn1-xMgxO films with wide band gap energy were paid much attention for many applications such as optic device, electric luminescence device and transparent conductive oxide of solar cell [1]. For the doping of magnesium atoms into Zn1-xMgxO films, this Zn1-xMgxO film had the wider band gap energy than that of ZnO film. The band gap energy of the Zn1-xMgxO films would be easily controlled by the magnesium content of this Zn1-xMgxO film. The Zn1-xMgxO films with the dopant of magnesium atoms present interesting electrical and optical properties, which find the wide applications in the fields of optoelectronic and transparent conductive oxide [2]. Other authors reported that Zn1-xMgxO films were deposited on the substrates by physical vapor deposition such as RF-magnetron sputtering, molecular beam epitaxy, metal organic chemical vapor deposition and pulsed laser deposition. On the other hand, the electrochemical preparation of oxide films from aqueous solutions presents several advantages over these techniques mentioned above; (1) the thickness and morphology of film can be controlled by electrochemical parameters, (2) relatively uniform films can be obtained on the substrates with complex shape, (3) films can be obtained on substrates with melting point below 373K such as polymer, (4) the technique is less hazardous and more environmentally friendly and (5) the equipment is not expensive. In this paper, the influence of zinc sulfate concentration on electrochemical growth of Zn1-xMgxO films will be discussed in detail. EXPERIMENT Zn1-xMgxO films were electrochemically grown on the conductive NESA glass (NESA glass, approximately 12Ω/□, Asahi glass Co., Ltd.) substrate from 0.1 mol/L Mg(NO3)2 aqueous solutions containing zinc sulfate ranging of 0.0 mmol/L to 5 mmol/L, at the deposition
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temperature of 323K, cathodic potentials of -0.9V. A Pt/Ti sheet (99.999% purity) was used as an active anode. An Ag/AgCl electrode was used as a reference electrode. The electrolysis was potentiostatically carried out by using a potentio/galvanostat without stirring. The structural properties of the
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