The influence of isothermal annealing on the optical and electrical properties of thin SnO2 films doped with fluorine

Abstract

In this paper, a comparative analysis of the effect of isothermal annealing (400°C) on optical transmission spectra, surface resistance and adsorption sensitivity to ethanol vapor of tin oxide films doped with fluorine ions and films obtained without the addition of a fluorinating agent, is carried out. An increase in the transparency of the films is shown during annealing for 3 hours. Further annealing leads to a significant decrease in the transparency of thin films. The band gap calculated from the transmission spectra corresponds to the value of the band gap of SnO2 at room temperature (Eg = 3.6 eV).The value of the gap width of films obtained from the sol with the addition of NH₄F, with the duration of annealing varied within the accuracy of the measurements. With increasing duration of film annealing, the surface resistance increases. Films obtained from the sol with the addition of NH₄F have a lower surface resistance than films obtained from the sol without additives. This is confirmed by the presence of fluoride ions in the films as additional sources of free charge carriers. It is shown that an increase in the annealing time at 400°C to three hours leads to an increase in the surface resistance and a decrease in the sensitivity to ethanol vapor. This, perhaps, is associated with the reduction of small defects and the rupture of bonds between individual sol particles. Six-hour annealing at 400°C leads to an even greater increase in surface resistance and an increase in sensitivity to ethanol vapor. Perhaps this is due to the appearance of microcracks and the destruction of individual sol particles.