Fabrication of aluminium doped zinc oxide (AZO) transparent conductive oxide by ultrasonic spray pyrolysis Rina Pandey, Shavkat Yuldashev, Hai Dong Nguyen, Hee Chang Jeon, Tae Won Kang * Department of Physics, Dongguk University, 26-3 Pildong, Chungku, Seoul 100-715, South Korea article info Article history: Received 7 December 2011 Received in revised form 9 May 2012 Accepted 14 May 2012 Available online 24 May 2012 Keywords: Transparent conductive oxide Al doped ZnO Ultrasonic spray pyrolysis abstract In this work, we studied aluminium doped zinc oxide (AZO) and an annealing treatment on electrical and optical properties of films prepared by ultrasonic spray pyrolysis. In comparison with conventional methods, ultrasonic spray pyrolysis method provides advantages such as low equipment cost, good thickness uniformity over a large area, low temperature and low vacuum requirement in processing. Aluminium doped ZnO films were deposited on glass substrates with different doping concentrations. Detailed structural, electrical and optical measurements were conducted to resolve the effects of aluminium doped ZnO films. The resistivity was w10 3 U cm, carrier concentration w10 20 cm 3 and mobility w7 cm 2 /Vs. The optical transmittance of films was higher than 80% and optical band-gap energy increases from 3.25 eV to 3.54 eV. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Transparent conducting oxide (TCO) films have been widely studied for transparent and flexible device applications such as liquid crystal displays, plasma display panels, electronic paper displays, organic light emitting diode, solar cells, touch panels, gas sensors and other optoelectronics devices [1]. The most commonly used TCO material is indium tin oxide (ITO), because of its high conductivity and optical transparency over visible wavelengths [2]. However, there is a large amount of research into alternative TCO materials, because of the relative scarcity and high cost of indium [1]. One of the most commonly cited alternative materials is zinc oxide. Zinc oxide has the direct band-gap of 3.37 eV at room temperature, which has great potential in blue and ultraviolet (UV) photo electronic applications: such as UV detectors, transparent high power electronics, and short wavelength device. It is a wurt- zite-type semiconductor having large exciton binding energy of 60 meV at room temperature. Furthermore, the ZnO is great optional transparent conducting oxide with the average trans- parency (T > 80%) and resistivity (<10 3 U cm). Compared with ITO, ZnO is lower cost material with no toxicity, and stable at high temperature. It has attracted considerable interest because of its excellent performance in devices pertaining to optics, electronics, and photonics [3]. Numerous methods are used to fabricate AZO thin films, such as pulsed laser deposition [4], RF magnetron sputtering [5], atomic layer deposition [6], spray pyrolysis [7,8], and solegel [9]. Among these methods, the spray pyrolysis technique has several advan- tages over the others such as deposition of high purity, homoge- neous, simplicity, safety, large area films, the low cost of the apparatus and the raw materials. The n-type conductivity in non- stoichiometric ZnO is well known to originate from zinc intersti- tials and oxygen vacancies. Between the above mentioned two mechanisms, the formation of carriers by the ionization of zinc interstitials has been acknowledged to be predominant in intrinsic ZnO crystals. In addition, the increment in the number of carriers in ZnO crystals was achieved by thermal treatment with hydrogen [8] or by an appropriate doping process [9e12]. In this paper, we present the effects of impurity elements of group III aluminium (Al) and an annealing treatment on electrical and optical properties of aluminium doped zinc oxide (AZO) thin films prepared by ultrasonic spray pyrolysis method. Detailed structural, electrical and optical measurements were conducted to resolve the effects of aluminium doped ZnO films. Also, optimal composition of aluminium content was researched for application of transparent conducting electrode. 2. Experimental details The aluminium doped ZnO films were deposited on glass substrates by ultrasonic spray pyrolysis method. The glass substrate was ultrasonically cleaned in acetone, methanol and rinsed in * Corresponding author. E-mail address: twkang@dongguk.edu (T.W. Kang). Contents lists available at SciVerse ScienceDirect Current Applied Physics journal homepage: www.elsevier.com/locate/cap 1567-1739/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.cap.2012.05.027 Current Applied Physics 12 (2012) S56eS58