Gas sensing properties of c-axis-oriented Al-incorporated ZnO films epitaxially grown on (11-20) sapphire substrates using pulsed laser deposition

Al-incorporated ZnO films with various Al concentrations were prepared using pulsed laser deposition on the (11-20) face of sapphire substrates, and their gas sensing properties were evaluated. The use of c-axis-oriented epitaxial films with the same thickness suppressed the influence of the surface-to-volume ratio and surface atomic arrangements on the sensing properties, clarifying the role of Al doping in the improvement of ZnO gas sensors. The results of ethanol gas sensing measurements indicated that Al doping significantly improved the sensing response and response time of the ZnO gas sensors. The formation of Al-related impurity phases and/or non-equilibrium defects induced by Al doping improved the sensing performance. On the other hand, changes in the grain size did not significantly affect the sensing response.