Undoped tin oxide thin films obtained by the sol gel technique, starting from a simple precursor solution

In this work, we report the synthesis and the structural, optical and electrical properties of undoped tin oxide thin films obtained by the sol-gel technique. The films have been prepared from a simpler precursor solution than other ones reported; it is based on stannous chloride (SnCl2 center dot 2H(2)O), ethanol, glycerol and triethylamine. The films are deposited on glass slide substrates and sintered at temperatures in the 300-550 A degrees C range, in an open atmosphere. A second thermal treatment in vacuum is made in order to decrease the resistivity of the films. The X-ray diffraction patterns show the tetragonal phase of SnO2 with a small preferential orientation in the (110) plane. All films show high optical transmission (similar to 85%) and a direct band gap value around of 3.8 eV. The minimum resistivity value, 2 x 10(-1) Ohm-cm, is obtained for the films sintered at 300 and 350 A degrees C and thermal treated in vacuum at 500 A degrees C for 1 h. The decrease of the resistivity with the thermal treatment in vacuum is associated with an increase in the oxygen vacancies concentration.