Fluorine-doped tin oxide films with a high figure of merit fabricated by spray pyrolysis
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l Ramírez Amador Mechatronics Department, Universidad Tecnológica de Huejotzingo, Puebla 74169, Mexico (Received 12 November 2014; accepted 22 April 2015)
Fluorine-doped tin oxide (FTO) thin films were deposited by spray pyrolysis in a pulse mode at 450 °C on glass substrates, using an alcoholic solution of SnCl45H2O and NH4F with different F/Sn ratios in the precursor solution. The film structure was nanocrystalline for all molar F/Sn ratios in the solution from 0 to 1.0. Postdeposition annealing treatments were not carried out. The films with a F/Sn 5 0.35–1.0 ratio present a high grain orientation in the (200) crystallographic plane. A minimum sheet resistance of 4.5 X/sq, a resistivity of 2.2 104 X cm, a maximum electron mobility of 21.6 cm2/V s, and a carrier concentration of 1.7 1021 cm3, corresponding to a strong degeneration of the electron gas in the conduction band, as well as a mean value of the transmittance of 0.84 in the visible spectral range, were obtained for the films fabricated with a F/Sn 5 0.5 ratio. A high value of the figure of merit was obtained using two methods (38.8 103 X1 and 5.75 X1), that is, comparable with the highest values reported to date.
I. INTRODUCTION
Contributing Editor: Paul Muralt a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.138
emissivity coatings for windows, gas sensors, and transparent conducting layers in liquid crystal displays. Chemical vapor deposition (CVD) is one of the most commonly used techniques for the production of FTO films. This method involves the transport of gaseous precursors (inorganic or organic) to a reactor for their subsequent decomposition on the heated substrate. Hence, it is a relatively simple, versatile, and reproducible process that gives high quality thin film products.2 A simpler analog of the CVD process is the spray pyrolysis, a technique that is well suited for the preparation of doped tin oxide films because of its inexpensive experimental arrangement, easy of adding various doping materials, reproducibility, high growth rate, and possibility of adaptation for mass production to obtain large area coatings.3 From many published results, it can be observed that the structural, electrical, and optical properties of the FTO films depend strongly on the deposition conditions. Both the optical transmission and electrical conductivity of the films should exceed a certain minimum value. Ideally, both parameters should be as high as possible. However, a simultaneous achievement of maximum transmission and conduction is not possible in most cases. This makes important a quantitative comparison of the performance for TCO films presenting different thicknesses, morphological structures, as well as electrical and optical parameters fabricated with different technological methods and substrates. A better balance between optical transmission and sheet resistance, important for numerous applications,
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Ó Materials Research Society 2015
It is well-known that many wide gap stoichiometric oxide mat
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