Sn-Doped In 2 O 3 Nanocrystalline Thin Films Deposited by Spray Pyrolysis: Microstructural, Optical, Electrical, and For
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N.G. Pramod, S.N. Pandey, and P.P. Sahay (Submitted February 8, 2013; in revised form April 3, 2013) Undoped and Sn-doped (1, 1.5 and 2 at.%) indium oxide (In2O3) thin films have been grown by the chemical spray pyrolysis technique on cleaned glass substrates using indium nitrate [In(NO3)3] and stannic tetrachloride hydrated (SnCl4Æ5H2O) as the host and dopant precursors, respectively, and deionized water as the solvent. Structural characterization using x-ray diffraction reveals that the films possess cubic structure, with the average crystallite size in the range 10-14 nm. The surface morphology and roughness of the films have been investigated by means of an atomic force microscope. UV-Vis measurements indicate an enhancement in the optical transmittance in the visible region on Sn doping. Further, the doping effect has been found to substantially reduce the electrical resistance to a few orders of magnitude of the undoped In2O3 film. We report a simultaneous improvement in both the optical and electrical properties of indium oxide thin film due to the doping of Sn ions. These results indicate that Sn-doped In2O3 thin film can be a potential candidate for use in various optoelectronic devices. Among all the films examined, the 1 at.% Sn-doped film shows the maximum response (~91%) at 300 C for 80 ppm concentration of formaldehyde in air.
Keywords
formaldehyde sensor, Sn-doped In2O3 film, spray pyrolysis, structural and optical properties
1. Introduction Indium oxide (In2O3) thin film has drawn a great deal of attention from researchers due to its excellent optical transparency and electrical conducting properties. In2O3 is an important n-type transparent conducting oxide (TCO) possessing both direct band gap (3.5-3.7 eV) (Ref 1) and an indirect band gap (~2.6 eV) (Ref 2). Films of In2O3 have been used as flat panel displays (Ref 3, 4), solar cells (Ref 5), and also as gas sensors (Ref 6, 7). Morphology and size distribution of In2O3 nanoparticles play an important role in deciding the properties of nanoparticle thin films. To obtain low resistive films, a number of metal ions have been used as dopants. Parthiban et al. (Ref 8) and Elangovan et al. (Ref 9) have studied the effect of molybdenum doping on indium oxide thin films for solar cell applications. Zhang et al (Ref 10) have investigated the dependence of electrical and optical properties on the
N.G. Pramod, S.N. Pandey, and P.P. Sahay, Department of Physics, Motilal Nehru National Institute of Technology, Allahabad 211004, India. Contact e-mail: dr_ppsahay@rediffmail. com.
Journal of Thermal Spray Technology
film thickness of tungsten-doped indium oxide thin films. Kim and Choi (Ref 11) have studied Eu-doped ITO thin films by the sol-gel technique. The characteristics of zirconium-doped In2O3 thin films prepared by magnetron sputtering have been studied by Zhang et al. (Ref 12). Mg-doped indium oxide thin films have been studied by Raj et al. (Ref 13). Sprayed In2O3 thin films as a methanol sensor have been reported for the first time by our group (Re
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