Effect of Aluminum Nitrate Concentration in Zinc Acetate precursor on ZnO:Al thin films prepared by spray pyrolysis
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Effect of Aluminum Nitrate Concentration in Zinc Acetate precursor on ZnO:Al thin films prepared by spray pyrolysis Samerkhae Jongthammanurak1, Sirirak Phakkeeree2, Yot Boontongkong1 and Chanchana Thanachayanont1 1
National Metal and Materials Technology Center, 114 Thailand Science Park, Pahonyothin Rd., Klong 1, Klong Luang, Pathumthani 12120, Thailand 2 Department of Materials Engineering, Kasetsart University, Bangkok Thailand ABSTRACT Aluminium-doped zinc oxide (ZnO) films have been prepared by spray pyrolysis technique using the mixed solution of zinc acetate dihydrate and aluminium nitrate nonahydrate in methanol. Concentration of aluminum in the solution was varied in a range of 1, 3 and 5 atomic percent. The results from X-ray diffraction showed that the preferred orientation of ZnO films changed to the [002] direction when the concentration of aluminum in the solution exceeded 1 atomic percent. ZnO films deposited from the 3 atomic percent Al containing solution had the largest grains and showed the lowest resistivity of 75 Ω-cm. Addition of aluminum into the precursor solution shifted the absorption edge towards longer wavelengths. INTRODUCTION Transparent conductive oxide (TCO) offers advantages of electrical conductivity and transparency to visible light. Indium tin oxide (ITO) thin films have been widely used in making electrodes of photovoltaic and optoelectronics devices [1-4]. However, rising cost of ITO in the last five years necessitates the replacement of ITO with cheaper materials in order to keep the devices in reasonable price. ZnO is an attractive candidate for the substitution because of its abundance. Doping of Ga, In, Sn and Al into ZnO thin films is demonstrated to decrease the electrical resitivity [1, 5-8]. The ZnO thin films can be deposited by magnetron sputtering [8-12], pulse laser deposition [13], sol gel [14] and spray pyrolysis [15-20] techniques. Al-doped ZnO thin films deposited by magnetron sputtering demonstrate the electrical resistivity in the range of 10-4 Ω-cm [8-12]. They are used as electrodes in organic solar cells [8] and light emitting devices [9], showing performance comparable to ITO. The effect of Al doping concentration on the resistivity is investigated. The range of Al doping in ZnO films deposited by the spray pyrolysis technique is varied from 0.1 to 5 atomic percent [15-18]. On the other methodology, the effect of film thickness on optical and electrical properties was studied in Al-doped ZnO films with Al doping concentration of 0.15 and 4 atomic percent [19, 20]. In the investigation of the effect of Al doping concentration on ZnO films, aluminium chloride was used as the dopant [15-18, 20]. In this study, we investigated the effect of aluminium concentration on ZnO thin film prepared by spray pyrolysis technique, by using aluminium nitrate as the dopant. Concentration of aluminum in the precursor solution was varied in a range of 1, 3 and 5 atomic percent. Preferred orientation in the [002] direction was observed in ZnO films doped with Al
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