Impact of Aluminum doping on the enhanced ethanol gas sensing characteristics of ZnO thin film

This study investigates the deposition of ZnO and 3 at. % Al-doped ZnO (Al@ZnO) films on glass substrates via the spin coating process, analyzing their structural, optical, morphological, elemental, surface, and gas sensing properties. X-ray diffraction revealed polycrystalline wurzite structures with c-axis orientation, albeit with decreased crystal quality upon Al doping. Optical measurements indicated an increased optical band gap from 3.265 to 3.291 eV after Al doping. Scanning electron microscopy confirmed altered grain structures with reduced sizes after Al doping, and a transition from hydrophilic to hydrophobic surface behavior (water contact angle: 86 +/- 5 degrees C for ZnO, 94 +/- 6 degrees C for 3 % Al@ZnO). Gas sensing measurements demonstrated maximum responses at different temperatures for ZnO and 3 % Al@ZnO, with the latter showing significantly enhanced response to ethanol vapor, indicating its potential for sensitive detection. 3 % Al@ZnO exhibited rapid response and recovery times (47 and 70 s, respectively, at 400 ppm ethanol exposure), detecting low ethanol concentrations with high sensitivity (gas response of 6.18 +/- 0.24 at 20 ppm ethanol) and stability over extended periods (up to 75 days). Furthermore, it demonstrated selectivity towards ethanol among tested vapors. These findings underscore the development of cost-effective gas sensors capable of detecting trace concentrations, such as 20 ppm of ethanol vapor. Density Functional Theory (DFT) calculations provided insights into the efficient binding of ZnO and Al@ZnO with ethanol, complementing the experimental results. Overall, this research contributes to advancing gas sensor technology for diverse applications requiring high sensitivity and selectivity.