Effect of Annealing and Surface Passivation on Doped SnO2 Thin FilmsPrepared by Spray Pyrolysis Technique

Abstract

In this study doped SnO2 thin films have been prepared by spray pyrolysis technique using an alcoholic precursor solution consisting of stannic chloride (SnCl4.5H2O), ammonium fluoride (NH4F) and palladium chloride (PdCl2). Optimization on the deposition parameters was done so as to obtain high quality thin films. The effect of varying the Fluorine content on the optoelectronic properties of F: SnO2 thin films was studied. Data for transmittance and reflectance in the wavelength range from 300nm – 2500nm was obtained using the solid spec 3700DUV spectrophotometer. Electrical characterization of the thin films was done using the four point probe method at room temperature. Post deposition treatment of the thin films by annealing in air then passivating in nitrogen gas environment was done in a tube furnace at 4500C. Sheet resistivity for the as prepared F: SnO2 was found to be 0.4599 Ωcm and 0.00075 Ωcm being the highest and lowest sheet resistivity at 22.74 at% F and 16.41at% F doping in SnO2 respectively. Low sheet resistivity of F: SnO2 thin films is due substitutional incorporation of F ions instead of oxygen ions into the crystal lattice of SnO2 thin films which increases free carrier concentration. The effect of annealing generally was found to improve on the electrical conductivity of the thin films which is due to increase in carrier mobility and density. Passivation on the other hand had a slight opposite effect. Effects of annealing and passivation on doped SnO2 thin films band gap energy and their transparency was insignificant, rendering the doped SnO2 thin films good choice for making a transparent thin film gas sensors.