Gas-sensing properties of indium-doped SnO2 thin films with variations in indium concentration

The dependence of sensitivity of SnO2 gas sensors on indium concentration has been studied. Undoped and indium-doped SnO2 gas sensors have been prepared by chemical vapor deposition (CVD) using SnCl4 as precursor solution without or with InCl3 as doping solution, respectively. The response of the sensors is observed to increase significantly with 20 wt.% InCl3 content towards 1000 ppm hydrogen, methanol, and carbon monoxide. Indium-doped SnO2 gas sensors with sensitivity as high as 17%, four times higher than that of undoped sensor, are obtained for 1000 ppm methanol. Above an amount of 20 wt.% InCl3, the sensitivity of the sensors decreases drastically. A concentration of 40 wt.% InCl3 decreases the response of the sensors down to the sensitivity value of the undoped sensor. Scanning electron microscopy (SEM) was used to investigate the morphology and pore structure of the undoped and indium-doped sensing films with variations in indium concentration. Further, the sensing films were characterized by X-ray diffraction (XRD) to identify the changes in their crystallographic structures. The relation between structure of the films and gas sensitivity is discussed. It is observed that structure of the sensors changes as the doping concentration increases.