The Structural, Optical and Electrical Properties of Spray Deposited Fluorine Doped ZnO Thin Films
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The Structural, Optical and Electrical Properties of Spray Deposited Fluorine Doped ZnO Thin Films Kondaiah Paruchuri1, Vanjari Sundara Raja1, Suda Uthanna1 and N. Ravi Chandra Raju2 Department of Physics, Sri Venkateswara University, Tirupati – 517 502, India 2 Department of Electrical Engineering, IIT Bombay, Mumbai – 400 085, India 1
ABSTRACT Highly transparent and conducting Fluorine doped zinc oxide thin films were deposited using spray pyrolysis method on glass substrates held at 450 0C. The X-ray diffraction study revealed that as the dopant concentration increases in ZnO films, the intensity of the preferential orientation of (002) reflection decreased and (101) was found to increase up to 5 at. % F. The crystallite size was varied from 40 to 50 nm with dopant concentration. The optical band gap of the un-doped films was 3.30 eV and it increased to 3.34 eV for 3 at. % F. The refractive index of the films was increased from 2.05 to 2.18 with the increase of dopant concentration from 0 to 5 at. %. The scanning electron microscopy results depicted that the microstructure of ZnO: F films highly influenced by the fluorine doping. After annealing the films in hydrogen atmosphere, the resistivity of the films decreased as increase the dopant concentration and it is 4×10-3 ȍ cm for 3at. % F beyond which it increased. The mobility of the charge carriers was 14 cm2/ V sec and the carrier concentration was 7.8×1019 cm3 obtained for the films doped with 3 at. % of fluorine concentration in the starting solution. INTRODUCTION Transparent conducting oxides (TCO) thin films have potential applications in various fields such as thin film solar cells, light emitting diodes and gas sensors [1-3]. Several metal oxide semiconductors such as In2O3, SnO2, ZnO and TiO2 have been employed to fabricate TCO films [4]. Among these, ZnO is most promising n-type semiconductor with wide direct band gap of 3.2 eV and have high exciton binding energy (60 m eV). It was alternative to Indium doped SnO2 (ITO) due to low cost, abundant, non toxicity and stable under hydrogen plasma [5]. Under normal conditions, ZnO shows n- type conductivity due to the presence of native defects like oxygen vacancies and/or interstitial Zn atoms [6]. The electrical conductivity can be improved by suitable dopants of cations and anions. Extensive work on doped ZnO thin films with cations such as boron, aluminium, gallium and indium has been reported [7-9]. However, there are few reports on fluorine (anion) doped ZnO thin films. ZnO thin films have been deposited by various techniques, such as sputtering [10], chemical vapour deposition [11], sol–gel [12], pulsed laser deposition [13], In addition to these techniques, spray pyrolysis method has received much attention because of its simplicity and cost-effectiveness as it does not require sophisticated vacuum apparatus [14]. In this investigation fluorine doped ZnO thin films deposited by using spray pyrolysis technique and study the influence of fluorine concentration in the starting solution on structural, op
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