Optical and electrical properties of tin oxide-based thin films prepared by streaming process for electrodeless electroc
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Optical and electrical properties of tin oxide-based thin films prepared by streaming process for electrodeless electrochemical deposition Farnood Khalilzadeh-Rezaie1, Isaiah O. Oladeji2, Gbadebo. T. Yusuf3, Janardan Nath1, Nima Nader4,5, Shiva Vangala4,5, Justin W. Cleary4, Winston V. Schoenfeld6, and Robert E. Peale1 1
Department of Physics, University of Central Florida, Orlando, FL 32816, U.S.A. SISOM Thin Films LLC, Orlando, FL 32805, U.S.A. 3 Department of Basic Sciences, Osun State Polytechnic, Iree, Nigeria 4 Air Force Research Laboratory, Sensors Directorate, Wright-Patterson Air Force Base, OH 45433, U.S.A. 5 Solid State Scientific Corporation, Hollis, NH 03060, U.S.A. 6 College of Optics and Photonics, University of Central Florida, Orlando, FL 32816, U.S.A. 2
ABSTRACT Transparent conducting thin-films of SnO2: F were grown on preheated glass, Al2O3 coated glass, and quartz substrates by Streaming Process for Electrodeless Electrochemical Deposition (SPEED). Stannic chloride (SnCl4) and ammonium fluoride (NH4F) dissolved in a mixture of deionized water and organic solvents were used as precursors. The preheated substrate temperature was varied between 440 and 500 °C. High quality SnO2:F films were grown at all the substrate temperatures studied. The resulting typical film thickness was 250 nm. X-ray diffraction shows that the grown films are polycrystalline SnO2 with a tetragonal crystal structure. The average optical transmission of the films was around 93% throughout the wavelength range 400 to 1000 nm. The lowest electrical resistivity achieved was 6 × 10-4 Ω-cm. The Hall measurements showed that the film is an n-type semiconductor, with carrier mobility of 8.3 cm2/V-s, and carrier concentration of 1 × 1021 cm-3. The direct bandgap was determined to be 4.0 eV from the transmittance spectrum. INTRODUCTION Transparent conducting oxides (TCOs) are wide band-gap semiconductors with relatively high free-electron concentration, which arises either from defects or extrinsic dopants with shallow levels near the conduction band edge [1, 2]. TCOs are increasingly used in photovoltaic (PV) devices and as electrodes, structural templates, and diffusion barriers. Indium tin oxide (ITO) is the most widely used TCO [3, 4] because of its high electrical conductivity and optical transparency. The expense of indium (In) motivates the search for alternative TCOs. Fluorine-doped tin oxide (FTO, or SnO2: F) is promising due to its chemical stability, electrical conductivity, optical transparency, and thermal stability, especially in hightemperature hydrogen-containing environments for gas sensing applications [5]. The microstructural, electrical, and optical properties of FTO are sensitive to deposition technique and conditions [6, 7]. Streaming Process for Electrodeless Electrochemical Deposition (SPEED) [8-11] is a high-rate uniform deposition technique that uses water-soluble precursors to rapidly coat the substrate with nanoparticle-based films. SPEED has is foundation in chemical bath deposition (CBD) [8-10] and is
