Non-additive influence of water vapor and lighting on the conductivity of tin dioxide film at room temperature

Subject and purpose of the study. The paper presents the results of experimental studies of the effect of water vapor and light intensity on the conductivity of a thin film of tin dioxide at room temperature. It is known that the use of illumination of active layers of sensors allows to reduce their operating temperature, which expands the application field of sensors and multisensor systems based on them. The aim of the paper is to investigate the joint influence of lighting and the effect of water vapor on the conductivity of tin dioxide films. Methods and materials. The sensitivity of gas sensors based on thin films of tin dioxide formed by a high-frequency magnetron method of sputtering a stoichiometric target SnO$_2$ was studied. The sensor was a rectangular alumina plate, on which parallel stainless steel contacts were formed. The length of the contacts is 10 mm, the gap between the contacts is 50 $\mu$m. The thickness of the active layer was 0.8 $\mu$m. Gas samples containing water vapor were prepared at the bubbler by bubbling of deionized water in stream of synthetic air. Content of water vapor in the gas sample was determined by the ratio in the stream of steam-air mixture and synthetic air. Results. It is shown for the first time that, at low illumination levels, the conductivity of a thin film of tin dioxide when gas samples are launched increases, and at high illumination levels, the conductivity decreases. A numerical calculation of the concentration and luxampere characteristics of gas sensitive structures is performed. Discussion. Results of calculations on the basis of proposed model showed that the increase or decrease in the conductivity of samples at a presence of test gas is determined by initial position of the Fermi level in the grain of a polycrystalline sample, which can be controlled by intensity of illumination. Conclusion. Results obtained can be used to create multisensor systems based on semiconductor layers for detection and recognition of gas impurities in the ambient atmosphere.