Studies on Photoresponse and LPG sensitivity of transparent Al doped ZnO thin films prepared by thermal evaporation technique

Abstract Undoped and Al doped ZnO thin films are prepared by thermal oxidation of vacuum coated Zn and Zn:Al metallic films at different concentrations of Al. The effect of Al doping on structural, optical and photoconducting properties of the films is studied by XRD, UV–vis spectroscopy and photoconductivity measurements. Both undoped and doped films possess polycrystalline hexagonal wurtzite structure with preferential orientation along (002) plane. The films are transparent (70%–90%) andpossess band gaps in the range 3.01 eV–3.29 eV. Enhanced electrical conductivity and improved photoconductivity are observed with increase in Al concentration,whereas the heavily doped ZnO samples show no appreciablesensitivity towards UV and visible light. The thermopower studies show the samples to be n -type conducting. Moreover, the Al doped ZnO exhibit improved gas sensitivity and response time to LPG detection, with that doped at 3 at% showing the best response time of ∼40s.