Enhanced H2S gas sensing properties of undoped ZnO nanocrystalline films from QDs by low-temperature processing

H2S gas sensitive films based on ZnO QDs of 3.8 nm were prepared through a spin-coating process. The sensitivity of ZnO films was greatly improved after low-temperature processing and grain sizes remained below twice Debye length. A modified flat band diagram was proposed to explain this great improvement. The comparison of responses of ZnO films annealed at different temperatures was made and the sensors exhibited quick response and recovery. The response of ZnO films toward H2S of 68.5 ppm was a relatively high value of 75 at room temperature, which reached its highest value of 567 at 90 °C. The optimal operating temperature of 90 °C is relatively low compared to other gas sensors based on ZnO. Meanwhile, ZnO films showed good selectivity toward H2S against SO2, NO2 and NH3.