Al3+-modified ZnO thin film sensor fabricated by the sputtering method: Characterization and a carbon monoxide gas detection study

Al: ZnO films are prepared by spraying from the pure ZnO and Al with doping at different weight ratios 0.01, 0.03, 0.05, and 0.09. X-ray diffraction, atomic force microscopy, and energy-dispersive X-ray spectroscopy are used to analyze the structural properties of the films. The results of X-ray diffraction prove that polycrystalline Al:ZnO with a hexagonal wurtzite structure is preferentially oriented on the c-axis, and this is further confirmed by transmission electron microscopy. In addition, 0.09 wt% of Al-doping shows high orientation and homogeneity with the (002) plane, which leads to an increase in the surface roughness properties of the thin films as the root main square by 57.4%. The annealing process at high temperatures increases the conductivity of the Al:ZnO films. The rate of electronic mobility increases slightly with low doping and decreases with increasing doping until it reaches its lowest value (0.1 cm2 (V.s)−1) at a doping ratio of 0.035 wt%. The samples show considerable response for CO at 80 ppm gas concentration with gas responses of 85% and 40% at 90 °C for 0.03 wt% Al:ZnO and ZnO films, respectively. The overall study observed that fabricated sensor Al3+-doped ZnO is reliable and very rapid in detecting carbon monoxide vapors at moderately high temperatures and low gas concentrations.