Influence of In doping on the structural, optical and acetone sensing properties of ZnO nanoparticulate thin films C.S. Prajapati, P.P. Sahay n Department of Physics, Motilal Nehru National Institute of Technology, Allahabad 211 004, India article info Available online 19 May 2012 Keywords: ZnO nanoparticulate thin films Structural and optical properties Acetone sensing properties abstract Indium-doped zinc oxide (ZnO) nanoparticle thin films were deposited on cleaned glass substrates by spray pyrolysis technique using zinc acetate dihydrate [Zn(CH 3 COO) 2 2H 2 O] as a host precursor and indium chloride (InCl 3 ) as a dopant precursor. X-ray diffraction results show that all films are polycrystalline zinc oxide having hexagonal wurtzite structure. Upon In doping, the films exhibit reduced crystallinity as compared with the undoped film. The optical studies reveal that the samples have an optical band gap in the range 3.23–3.27 eV. Unlike the undoped film, the In-doped films have been found to have the normal dispersion for the wavelength range 450–550 nm. Among all the films investigated, the 1 at% In-doped film shows the maximum response 96.8% to 100 ppm of acetone in air at the operating temperature of 300 1C. Even at a lower concentration of 25 ppm, the response to acetone in this film has been found to be more than 90% at 300 1C, which is attributed to the smaller crystallite size of the film, leading to sufficient adsorption of the atmospheric oxygen on the film surface at the operating temperature of 300 1C. Furthermore, In-doped films show the faster response and recovery at higher operating temperatures. A possible reaction mechanism of acetone sensing has been explained. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction Zinc oxide (ZnO), an n-type semiconductor with wide band gap of 3.37 eV at room temperature (300 K) and high exciton binding energy of 60 meV [1], has been shown to be one of the most attractive materials for gas sensor applications due to its thermal and chemical stability, abundance in nature, low cost and absence of toxicity [2–6]. ZnO has been exploited in various forms such as single crystal, sintered pellets, thick films, thin films and hetero-junctions [7–11]. More recently, this material has received a growing attention as a nanostructured material [12–15]. Morphology, size and size distribution of ZnO nanoparticles play an important role in deciding the properties of nanoparticulate thin films. One important method to modify the characteristics of the films is the introduction of dopants in the parent system, which, in turn, influences the performance of the gas sensors based on these films. Various dopants like Al, In, Cu, Sn, etc. have been used to improve sensitivity and selectivity perfor- mance of the gas sensors based on ZnO thin films [16–20]. Acetone has been in common use as a solvent and as an extracting regent in industry for several decades. Its speedy evaporation and toxic nature can make high concentrations in air dangerous to human health. At high concentration ( 410, 000 ppm) in air, acetone may cause such symptoms as cephalalgia, nausea and so on. Further, Acetone has been identified as a biomarker for type-I diabetes (T1D) [21]. In future, the possibility exists to use an acetone sensor as a means of monitoring the diabetic patient condition. Thus, there is the need of development of a reliable and selective acetone sensor. To the best of Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/mssp Materials Science in Semiconductor Processing 1369-8001/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.mssp.2012.04.015 n Corresponding author. Tel.: þ91 532 2271260; fax: þ91 532 2545341. E-mail address: dr_ppsahay@rediffmail.com (P.P. Sahay). Materials Science in Semiconductor Processing 16 (2013) 200–210