Effect of elevated substrate temperature on growth, properties, and structure of indium tin oxide films prepared by reac
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L. Vazquez Instituto de Ciencia de Materiales de Madrid (CSIC), C \ Sor Juana Inés de la Cruz N° 3, 28049 Madrid, Spain
A. Mücklich, U. Kreissig, R.A. Yankov, A. Kolitsch, and W. Möller Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf, 01314 Dresden, Germany (Received 19 January 2007; accepted 4 May 2007)
The paper correlates the growth and structure formation with the properties of indium-tin-oxide (ITO) films fabricated by pulsed reactive magnetron deposition onto amorphous substrates held at elevated temperatures ranging from room temperature to 510 °C. The evolution of the microstructure is consistent with the well-known structure zone model. The temperature dependence of the film texture is described with consideration of the interplay between the shadowing and surface-diffusion processes. It is shown that deposition at elevated temperatures lowers the crystallization threshold and is more effective in reducing resistivity than the postdeposition vacuum annealing at comparable temperatures. The films grown at a substrate temperature of 400 and 510 °C have the lowest resistivity of 1.2 × 10−4 ⍀ cm, the highest free electron density of 1.2 to 1.0 × 1021 cm−3, and mobility of 35–42 cm2 V−1 s−1 and exhibit the strongest (222) texture with the largest grain size.
I. INTRODUCTION
Thin films of indium-tin-oxide (ITO) are of interest for advanced applications in optoelectronics, solar cell, and liquid crystal display technologies.1 The major technical use of ITO is as a transparent conducting material. An optimal relationship between resistivity and transmittance is achieved for a crystalline ITO material due to the effect of activating the doping impurity. Therefore, either film deposition at elevated substrate temperature or postdeposition annealing is used to produce a crystalline material having the best combination of properties. For practical applications, film deposition by magnetron sputtering using compound (oxide) targets is presently the preferred preparation method. Accordingly, the emphasis in research has been primarily on studying ITO films produced in this way over the temperature range of
a)
Address all correspondence to this author. e-mail: [email protected] b) On leave from Physics Department, Kyiv National Taras Shevchenko University, Kyiv 01033, Ukraine. DOI: 10.1557/JMR.2007.0293 J. Mater. Res., Vol. 22, No. 8, Aug 2007
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room temperature (RT) to 400 °C. Earlier work has dealt with the optical and electrical properties of magnetron sputtered ITO films2,3 as well as with their structure4,5 and texture.6 A defect model at different donor impurity concentrations has been proposed7 to explain the electrical properties of the films. Work on detailed characterization of the defect structure of both bulk and nanocrystalline ITO has also been carried out.8 Recent studies have addressed the optical properties of porous nanocrystalline films9 and the effect of charge-carrier density on the film dielectric
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