Synthesis and characterization of Bi doped ZnO thin films using SILAR method for ethanol sensor S. Syed Zahirullah a,⇑ , P. Immanuel b , S. Pravinraj b , P. Fermi Hilbert Inbaraj b , J. Joseph Prince b a Department of Physics, M. I. E. T. Engineering College, Tiruchirappalli 620 007, Tamil Nadu, India b Department of Physics, Bharathidasan Institute of Technology, Anna University, Tiruchirappalli 620 024, Tamil Nadu, India article info Article history: Received 26 June 2018 Received in revised form 13 July 2018 Accepted 16 July 2018 Available online 17 July 2018 Keywords: Thin films Sensor Ethanol SILAR Bi doped ZnO abstract Pure and Bi doped ZnO thin films prepared by Successive Ionic Layer Adsorption and Reaction (SILAR) method. The structural analysis shows that prepared films are polycrystalline in nature with preferential orientation along (1 0 0), (0 0 2) and (1 0 1) planes. Scanning electron microscope shows the morphological changes of the films with respect to increase in doping concentration. The average optical absorption value of all films was in the near visible range and the band gap of the films varies from 3.21 to 3.17 eV. The gas sensing study shows a maximum response of the films at 1000 ppm of ethanol was found to be around 60% with an operating temperature of 400 °C. Ó 2018 Published by Elsevier B.V. 1. Introduction As concern with earlier report on oxide materials, zinc oxide (ZnO) has emerged as one of the promising candidate, due to its optical and electrical properties, high chemical and mechanical stability, abundance, which tends to lower material cost as com- pared with most currently used transparent conductive oxide materials like tin oxide and indium tin oxide [1]. ZnO, n-type semiconducting material with a direct band gap of 3.37 eV. ZnO thin films have been deposited using various techniques such as spray pyrolysis [2,3], Wet chemical [4,5], SILAR [6] etc. Among these techniques, SILAR method has received much attention because of its simplicity and cost-effectiveness. Bismuth an important impurity in ZnO helps boosting performance in opto- electronic applications. Because of larger radius of Bi atoms than Zn atoms, they produce large mismatch in lattice constants thereby conductivity of Bi doped ZnO material may greatly change to semi-insulating. However, to our knowledge, there are few reports dealing with Bi-doped ZnO films compared to other metal doped ZnO films. Therefore, in the present investigation, Bi-doped ZnO thin films have been deposited on the glass substrate by SILAR method. 2. Material and methods To synthesize pure and Bi doped ZnO thin films Zinc acetate dihydrate, Iso-propanol, Dietheanolamine and Bismuth Chloride were used as precursors with propanol as base solvent. For synthe- sizing pure ZnO thin film, 0.1 M of zinc acetate was dissolved in propanol and then calculated volume of DEA solution was added. For synthesizing Bi doped ZnO thin films, 1, 3 and 5% of Bismuth Chloride was dissolved in a mixture of distilled water and propanol separately and mixed with zinc acetates. Then calculated volume of DEA solution was added into each of the complex solution. The precursor solution was made to stirr for two hours at temper- ature of 60 °C until a clear and homogeneous solution is formed, and then aged for 24 h at room temperature (RT). The pre- cleaned glass substrates were first dipped in the precursor solu- tions for 30 s and then dipped in hot water (90 °C) for 30 s. The process was repeated for 50 cycles with retrieval period of 5 s on every dipping. Finally, the coated films were annealed at 400 °C under air atmosphere for an hour to obtain pure and Bi doped ZnO thin films. Finally the films were used for the Characterization and sensor studies. 2.1. Characterisation The structural analysis of the synthesized samples was carried out using a powder X-Ray diffractometer (PANalyticalX’Pert Pro) with the Cu-Ka radiation source (wavelength: 1.54 Å). UV–Vis https://doi.org/10.1016/j.matlet.2018.07.067 0167-577X/Ó 2018 Published by Elsevier B.V. ⇑ Corresponding author. E-mail address: syedzahirullah@gmail.com (S. Syed Zahirullah). Materials Letters 230 (2018) 1–4 Contents lists available at ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/mlblue