Al-doped ZnO thin films as methanol sensors

Al-doped zinc oxide (ZnO) thin films were prepared by chemical spray pyrolysis technique. The dopant concentration (Al/Zn at%) varied from 0 to 1.5 at%. Structural analysis of the films reveals that all the films are of polycrystalline zinc oxide in nature, possessing hexagonal wurtzite structure with (0 0 2) preferred orientation. The lattice constants calculated from the most prominent peaks are found to be in good agreement with the ICDD reference pattern: zinc oxide, 01-080-0074 (a = 3.2535 Å and c = 5.2151 Å). The sensing properties of the films towards methanol vapour are investigated for various concentrations of methanol in air at different operating temperatures in the range 200–350 °C. It is observed that compared to the undoped ZnO film, Al-doped films show higher sensitivity to methanol vapour. Among all the Al-doped films studied, the 0.5 at% Al-doped ZnO film shows the maximum response (∼44%) at 275 °C to 500 ppm of methanol vapour in air. Further, the films show fast response and recovery to methanol vapour at higher operating temperatures. The methanol-sensing mechanism of the film has been explained.