Optoelectronics properties of tin-doped indium oxide films fabricated by DC magnetron sputtering in pure argon with post
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report on the study of the characteristics of indium–tin oxide (ITO) films prepared by well-controlled and reproducible DC magnetron sputtering in argon with consequent annealing in oxygen atmosphere. The structural, electrical, and optical properties of the ITO films were investigated. It was found that the films deposited in argon atmosphere with a commercial ITO target have low transparency and high resistivity. The lower value of the resistivity around 3 104 X cm and the higher value of the figure of merit of 7.4 103 X1 for 200 nm thick films are obtained after postannealing the films at the optimal temperature T 5 300 °C for 1 h. It was found experimentally that postannealing at different temperatures allows tuning effective work function of the ITO films in the range of 4.2–5.5 eV. The latter is an important issue for applications in optoelectronic devices. The fabrication method is useful for the fabrication of ITO films with high electro-optical parameters on flexible polyimide substrates.
Contributing Editor: Winston Schoenfeld a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.159
oxygen partial pressure to obtain the required film parameters. Commercial ceramic ITO targets usually are fabricated from a mix of high-purity In2O3 and SnO2 powders (90 wt%:10 wt%), according to the solubility limits of Sn in In2O3 (12.4–15 mol% SnO2),7–9 using hydrothermal processes at temperatures below 1500 °C. The key issues for obtaining high-quality ITO films are correct sintering techniques. X-ray diffraction (XRD) peaks, chemical composition, and the coloration of the ceramic target are principal characteristics to be optimized in the correct formation of the ITO target. However, to the extent of our knowledge, these important parameters are not provided by manufacturers. National Renewable Energy Laboratory (NREL)15 and other researchers10 show that a thermal treatment in air or oxygen at 1300 °C leads to the formation of stoichiometry ITO targets having a light-green coloring similar to the color of mix of used powders, whereas a thermal treatment in reducing atmospheres (such as H2) results in a black coloring.15 This specific color of the target can be due to the presence of undesirable phases as metallic tin and/or blue–black tin suboxide SnO due to the dissociative decomposition of SnO2 in SnO 1 1/2 O2. The instable phase SnO can turn in Sn3O4 and pure Sn, whereas Sn3O4 will decompose in SnO2 and metallic Sn. It results in “black” color of the used target. That is why for receiving high-quality ITO films from commercially available targets, the oxygen additive is necessary. If only argon is used as the working gas for the sputtering, the stoichiometry deviation of the commercial “black” target will be reproduced in the films leading to
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Ó Materials Research Society 2015
I. INTRODUCTION
Transparent conducting oxides (TCOs) have been widely used as transparent electrodes for flat panel displays including liquid crystal displays, organic light emitting diodes (OLEDs), and pl
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