Effect of growth temperature on the key properties of aluminum-doped zinc oxide thin films prepared by atomic layer depo
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Research Letter
Effect of growth temperature on the key properties of aluminum-doped zinc oxide thin films prepared by atomic layer deposition Emine Güneri, Education Faculty, Erciyes University, 38039 Kayseri, Turkey Bethanie Stadler, Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN 55455, USA Address all correspondence to Emine Güneri at [email protected] (Received 24 April 2019; accepted 6 June 2019)
Abstract Aluminum-doped zinc oxide films were prepared by atomic layer deposition using diethylzinc, trimethylaluminum, and water. High-purity water was used with low vacuum. The effect of growth temperature on characteristics of the films was investigated. The crystallinity was improved as growth temperature was increased from 180 to 235 °C, with the grain sizes increasing from 32.830 to 47.020 nm. The films possessed high transparency with a 95% transmission window blue shifted with growth temperature. This shift was seen in the energyband gaps which changed from 3.46 to 3.68 eV, leading to a decreased resistivity from 1.52 × 10−5 to 1.28 × 10−5 Ω cm.
Introduction Transparent conducting oxides (TCOs) have been used to fabricate devices, such as photovoltaics,[1] touchscreens,[2] and liquid crystal displays,[3] because of high transparency in the visible spectrum and low resistivity.[4] Indium thin oxide,[5] galliumdoped indium zinc oxide,[6] zinc oxide (ZnO),[7] and aluminumdoped indium zinc oxide (AZO)[8] are typical TCO materials. Among these, AZO has attractive properties due to its lower cost for large area technology, the abundance of its component species, non-toxicity, and high stability in hydrogen plasma, thermal stability, and high transmittance at visible wavelengths.[8–12] Most importantly, AZO has been shown to have high transmission (80%–90%) in the visible while having fairly low resistivities (10−4 to 10−3 Ω cm). AZO-coated substrates have been prepared by a variety of methods including pulsed laser deposition (PLD),[9] sol–gel,[10] radio-frequency magnetron sputtering,[11] and atomic layer deposition (ALD).[12] Among these, ALD has the best thickness and doping level control, extremely smooth and pinhole-free surfaces, and easy mass production.[13] Here, the goal was to achieve low resistivity while maintaining high transparency. To do this, very high purity water, low pressures, and high nitrogen flow rates were used at deposition temperatures to determine the effect on the structure, surface morphology, and electrical–optical properties of ALD-AZO thin films.
Experimental Transparent, conductive AZO thin films were deposited on Corning glass substrates using a Savannah series from Cambridge Nano Tech Inc. (MA/USA) at various growth temperatures (180–235 °C). The frequency ratio of Zn–O and Al– O cycles was constant at 19/1 to obtain AZO thin films with
999 layers per film. Diethylzinc, trimethylaluminum, and highpurity H2O were used as precursors of zinc, aluminum, and oxygen, respectively. During deposition, high-purity nitrogen gas with a flow rate of
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