Conductivity enhancement by fluorine doping in boron-doped ZnO thin films deposited by the electrospraying method

Abstract

ZnO thin films co-doped with boron and fluorine (B, F-ZnO) were deposited by the electrospraying method onto a heated glass substrate. The characteristics of the films were investigated as a function of dopant concentrations in the solution. X-ray diffraction studies revealed that all the prepared films were polycrystalline in nature and exhibited the ZnO hexagonal wurtzite structure with preferential orientation along the (002) crystal plane. In addition, shift in the XRD patterns was observed and the crystal orientation was changed at a certain amount of fluorine ( > 6 at%) in the starting solution. Analyses of X-ray diffraction and X-ray energy dispersive patterns demonstrate that fluorine and boron have been successfully doped into the ZnO thin films. Like these studies, the scanning electron micrographs showed that the grain size tends to decrease by the addition of fluorine. It was also observed that 2 at% boron and 6 at% fluorine was the optimal amount in order to achieve the minimum resistivity and maximum transmittance. The minimum value of resistivity of about 1.01 x 10 (-4) Omega cm and high optical transmittance of 98% in the visible region were obtained for 2 at% boron and 6 at% fluorine co-doped ZnO films. Moreover, the present values of resistivities are closest to the lowest resistivity values among the doped ZnO films and also closer to the indium tin oxide (ITO) resistivities that were previously reported. We confirmed that the boron and fluorine atoms substitution in the ZnO lattice imparts positive effects in terms of enhancing the free carrier concentration and density of films, which will further improve the electrical and optical properties. The films produced at optimum conditions are suitable for optical and electrical applications owing to their low resistivity and high optical transmittance in the visible range. (C) 2012 Elsevier B.V. All rights reserved.