The role of doping effect on the response of SnO2-based thin film gas sensors: Analysis based on the results obtained for Co-doped SnO2 films deposited by spray pyrolysis

Effect of doping by cobalt on gas sensing, electrophysical and structural properties of the SnO2 films was studied. Undoped and doped SnO2 films were deposited by spray pyrolysis method on alumina, silicon and quartz substrates kept at 410–450 °C. The film structure was controlled by XRD and SEM methods. Ozone and hydrogen were used as tested gases. It was found that the influence of doping by cobalt on the SnO2-based gas sensor parameters depends on the concentration of doping additives and could be accompanied by either improvement of sensor parameters at low level of doping (CCo < 2–4%) or degradation of the gas sensor operation characteristics while concentration of additives exceeds 2–4%. It was given an explanation of observed effects. In particular, it was shown that structural changes caused by incorporation of cobalt in the SnO2 lattice was the main factor, controlling the change of the SnO2 gas sensing properties during the process of the SnO2 bulk doping.