High Mobility Nanocrystalline Indium Zinc Oxide Deposited at Room Temperature
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High Mobility Nanocrystalline Indium Zinc Oxide Deposited at Room Temperature E. Fortunato, A. Pimentel, A. Gonçalves, A. Marques, R. Martins Materials Science Department/CENIMAT, Faculty of Sciences and Technology of New University of Lisbon and CEMOP/UNINOVA, Campus da Caparica, 2829-516 Caparica, Portugal.
ABSTRACT In this paper we present results of indium doped zinc oxide deposited at room temperature by rf magnetron sputtering, with electron mobility as high as 60 cm2/Vs. The films present a resistivity as low as 5×10-4 Ωcm with an optical transmittance of 85%. The structure of these films look-like polymorphous (mixed of different amorphous and nanocrystalline phases from different origins) as detected from XRD patterns (no clear peak exists) with a high smooth surface, as detected from SEM micrographs, highly important to ensure long life time when used in display devices.
INTRODUCTION Nowadays we are facing a large increase related to the sophistication of transparent conducting oxides (TCOs) used as transparent electrodes for optoelectronic devices, such as flat panel displays, solar cells, electrochromic devices and image sensors. The primary demands for such materials are: have high optical band gap (>3.5 eV), good electrical conductivity (>103 Scm-1), high optical transparency (> 80% in the visible region and in some cases near the infrared region), good etchability and process compatibility for micropatterning, surface uniformity (especially with amorphous phase) and chemically and thermally stable in various environments. At present indium tin oxide (ITO) is the most used TCO material, basically for presenting most of the previous requirements [1]. Nowadays the emphasis is put in processing such layers with high electronic and optical performances at low temperatures, to be compatible with emerging organic related technologies, such as flexible electronics where low cost polymeric substrate are intended to be used in disposable device applications. To reach such goal, new materials and systems, with particular emphasis to the system based on indium-zinc oxide (IZO) [2-7] start being studied aiming to take advantage of both In2O3 and ZnO structures. In the present work we present data on the role of the rf power on the structural and physical properties of IZO thin films deposited at room temperature by magnetron sputtering.
EXPERIMENTAL DETAILS The indium zinc oxide (IZO) films were deposited onto soda lime glass substrates by rf (13.56 MHz) magnetron sputtering using a ceramic oxide target ZnO/In2O3 (10:90 wt%; 5 cm diameter) from Super Conductor Materials, Inc. with a purity of 99.99%. The sputtering was carried out under room temperature, with a partial pressure of oxygen varying from 2.1×10-3 Pa
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and a total deposition pressure (argon and oxygen) of 0.15 Pa. The distance between the substrate and the target was 10 cm and the rf power was varied between 100 W and 175 W. The film thickness (d) was measured using a surface profilometer (Dektak 3D from Sloan Tech.). The electrical
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