Correlation Between Structural, Electrical, and Optical Properties of ZnO:In for Ethanol Gas Sensing Application

Indium-doped zinc oxide (ZnO:In) thin films were prepared using the spray pyrolysis technique, and the effects of indium concentration on the structural, optical, electrical, and sensing properties of the ZnO:In films were investigated. The indium concentration was varied between 0 wt.% and 15 wt.%. The results show a polycrystalline structure for all layers using x-ray diffraction. The lowest sheet resistance of approximately 120 Ω/□ was achieved with an indium concentration of 5 wt.% in the starting solution. The morphological properties of the thin films were investigated using field-emission scanning electron microscopy. The results indicate that an increase in the indium concentration disrupts the nano-granular structure of the surface, the surface becomes wrinkled, and a snowflake-like pattern is formed on the surface of the thin film. The ethanol sensing properties of the samples were studied using an electric circuit. Sensing parameters including the dynamic response, sensitivity, and response/recovery times of the samples were investigated. For an ethanol concentration of 200 ppm, the gas response of the pure ZnO layer was about 1.05. An increase in the indium concentration to 15 wt.% was found to improve the gas response of the samples. For an ethanol concentration of 200 ppm, the gas response of the ZnO:In (15 wt.%) layer increased to 1.82.