Texture coefficient and band gap tailoring of Fe-doped SnO 2 nanoparticles via thermal spray pyrolysis Majibul Haque Babu, Bidhan Chandra Dev, Jiban Podder* Received: 26 April 2018 / Revised: 1 July 2018 / Accepted: 10 April 2019 Ó The Nonferrous Metals Society of China and Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract An investigation of Fe-doping effect on SnO 2 thin films was performed in this study using thermal spray pyrolysis (TSP) method. The surface morphology and structural, optical and electrical properties were studied by field energy scanning electron microscope (FESEM), X-ray diffraction (XRD), ultraviolet–visible (UV–Vis) spec- troscopy and four-point probe method. FESEM images demonstrate that the surface morphology of the as-de- posited films varies when Fe-doping content varies. XRD studies reveal that crystallite size and preferential growth orientations of the films are dependent on Fe-doping con- centrations. The grain size is found to decrease with the increase in Fe content. These studies also specify that the films have tetragonal rutile-type structure with mixed sec- ondary phases. The texture coefficient value of (110) plane increases with the concomitant in-plane (220) decrease in higher doping concentrations. The resistivity and the optical absorbance are found to increase with Fe concen- tration. The direct optical band gap decreases from 3.94 to 3.52 eV with increasing Fe content. Keywords SnO 2 thin film; Thermal spray pyrolysis; Texture coefficient; Optical band gap 1 Introduction Transparent conducting oxide (TCO) materials are of great importance due to their supreme features such as higher transmittance in the ultraviolet–visible (UV–Vis) region, higher reflectance in infrared region, higher electrical conductivity, deficiency of toxicity, easy tailoring and abundant nature [1, 2]. TCO materials have numerous applications such as electrode materials in solar cells [3], flat panel displays [4], transistors [5], light-emitting diodes [6], gas sensors [7], high-density energy storage material [8], high-performance capacitor [9], dynamic random-ac- cess memory (RAM) [10], electrode ceramics [11], lithium batteries [12], resistors [13] and transparent heaters [14]. SnO 2 is one of the TCO materials which has been com- prehensively used as an n-type semiconductor along with wide direct band gap of 3.6 to 4.1 eV [15]. However, the physical properties of SnO 2 can be improved by suit- able dopants like Al [16], Mn [17], Fe [18], Sb [19], etc. The transition metal (TM-3d) ions as dopant atoms with open d-shell have numerous physical properties of their host materials. Fe is one of the best suitable dopants of the SnO 2 lattice structure to obtain good-quality thin films for optoelectronic device applications [20]. In addition, oxy- gen vacancies are produced in SnO 2 lattice structure by Fe- doping. The oxygen vacancies have an immense influence on the physical properties of SnO 2 film and strongly attract the Fe atoms. Consequently, the TM–oxygen vacancy–TM groups are formed in Fe-doped SnO 2 films. A variety of deposition techniques of film like chemical vapor deposi- tion, thermal evaporation, pulse laser deposition (PLD), spray pyrolysis, sol–gel coating and hydrothermal method have been used to prepare pristine and doped SnO 2 film [21, 22]. Among these techniques, the thermal spray pyrolysis is a beneficial method to obtain the intended thin films as this is a simple and cost-effective experimental setup, with ease of adding acceptor-doping materials, reproducibility and mass production capability for uniform large area deposition. In this present work, Fe-doping M. H. Babu, B. C. Dev, J. Podder* Department of Physics, Bangladesh University of Engineering and Technology, Dhaka 1000, Bangladesh e-mail: jpodder59@gmail.com 123 Rare Met. RARE METALS https://doi.org/10.1007/s12598-019-01278-3 www.editorialmanager.com/rmet