Structural, optical, electrical and room temperature gas sensing characterizations of spin coated multilayer cobalt-doped tin oxide thin films

The negative charge trapped in the oxygen species present in metal oxides like Tin Oxide (SnO2) caused an upward band bending and makes these materials as promising sensing materials for CO2 detection. However, sensors based on pure SnO2 may only detect CO2 at high temperature making them un-sensitive at room temperature (RT) (20 degrees C). In this study, SnO2 and Cobalt doped SnO2 (Co:SnO2) thin films of varying thickness were successfully synthesized by sol-gel spin coating technique, followed by annealing. The highly active surface due to high number of divided layers has been determined by X-ray diffraction (XRD) for neat and doped SnO2 deposition. Moreover, the effect of increasing the annealing from 400 to 500 degrees C has been evaluated. The calculated band gap of the multilayer sample annealed at 500 degrees C blue shifted from 3.55 to 3.81 eV with the Co doping. Therefore, the Co doped SnO2 can detect CO2 as low as 30 vol% in atmosphere at RT, meanwhile the un-doped SnO2 coating shows a weak response. Moreover, at high CO2 concentration the recovery time decreases due to the high desorption kinetic. The obtained results illustrate the control of the film's properties gives the opportunity to manage the sensing and optoelectronic performance.