Preparation and properties of sprayed undoped and fluorine doped tin oxide films

Thin films of undoped and fluorine doped tin oxide have been prepared on borosilicate glass plates by a spray pyrolysis technique. The effect of process parameters, such as tin chloride concentration in the precursor solution, substrate to nozzle distance, carrier gas (air) flow rate, substrate temperature, and doping level of fluorine in the spray solution, on the physical properties of the tin oxide thin films have been investigated. The grown films were polycrystalline in nature above 350°C, the [110] reflection having the maximum intensity in all cases. Films of about 10−3 Ω cm resistivity and high visible transparency of about 88% have been obtained at the optimum substrate temperature of 425°C and fluorine doping concentration of 57 at.%. The optical investigations show that the optimized films have a direct allowed bandgap of 4.25 eV and indirect allowed bandgap of 2.71 eV.