Characterization of SnO2 thin films through thermoelectric power measurements

SnO2 thin films deposited by spray pyrolysis, using SnCl2 as precursor solution and HF as source of the doping impurities, were characterized through Hall Voltage, thermoelectric power (alpha) and conductivity (sigma) measurements at room temperature, in order to determine the influence of the incorporation of F-impurities on the electrical transport properties. Non doped SnO2 films with resistivities of 2.8 x 10(-3) st cm were grown at 400 degrees C and their resistivity was decreased to 3 x 10(-4) Omega cm adding HF to the precursor solution. It was found that the resistivity is dominated by the resulting carrier concentration, which is controlled by incorporating of Cl- and/or F- impurities in anion sites of the SnO2 lattice. Carrier concentrations of about 3 x 10(19) cm(3) were obtained with non doped SnO2 samples, which were increased to about 5 x 10(21) cm(-3) by adding HF to the precursor solution in concentrations corresponding to a [F-ions]/[Sn-ions] ratio of 1. The corresponding mobility decreased significantly by increasing the concentration of F-ions in the spraying solution. The study also revealed that the interactions of free carriers with ionized impurities and with optically polarized phonons, are the scattering mechanisms which more strongly affect the electrical transport processes at room temperature in SnO2:F films deposited by spray pyrolysis. (C) 1999 Elsevier Science S.A. All rights reserved.