Ethanol sensing characteristics of sensors based on ZnO:Al nanostructures prepared by thermal oxidation

ZnO and ZnO:Al nanostructure were synthesized and fabricated as ethanol gas sensors. For FE-SEM images, the diameter and length measured at the middle of the wire-like structure were in range of 100-500 nm and several micrometers, respectively. From TEM analysis, it was suggested that the ZnO:Al nanostructure grew along (112̅0) direction on [0001] plane. The Raman spectra of ZnO and ZnO:Al nanostructures can confirm existence of defect effects due to oxygen vacancies and Zn interstitials of ZnO. Besides, it also suggested that the ZnO:Al nanostructures had (112̅0) direction perpendicular to the surface. The ethanol sensors based on ZnO:Al nanostructure sensors can be improved when compare with pure ZnO nanostructure sensor at the ethanol concentrations of 50-1000 ppm. The highest sensitivity of 32 was obtained in ZnO:Al nanostructure sensors with Al 1% by mol compared to 14 of pure ZnO nanostructure sensor at optimum temperature of 300°C. The sensitivity improvement of ZnO:Al sensors can be explained by an increase of oxygen vacancy-related defects which increase the surface depletion layer width as described in sensitivity equation. The larger surface depletion layer width results in higher the potential barrier height at the contacts and finally, sensitivity improvement.