Tailoring of optical and electrical properties of transparent and conductive Al-doped ZnO films by adjustment of Al concentration

Highly optically transparent and electrically conductive Al-doped ZnO (AZO) thin films with varied Al concentrations were synthesized by means of reactive deposition of ZnO host films and in-situ doping of Al by pulsed laser co-ablation of a Zn target and an Al target with the assistance of an oxygen plasma. The optical and electrical properties of AZO films were tailored by the adjustment of Al concentration which was realized by varying the laser fluence on the Al target. The morphology, composition and structure as well as the optical and electrical properties were characterized and the effects of Al doping and post-deposition annealing were investigated. Similar with undoped ZnO, the synthesized AZO films have a hexagonal wurtzite structure with the crystallinity deteriorated, present high visible transparency with the absorption edge blue shifted and show good electrical properties with the electrical conductivity increased. The structural, optical and electrical properties are strongly dependent on Al concentration and are significantly improved after annealing in H₂/N₂ mixed gas. Annealed AZO films containing 3.0 at% Al haveoptical properties including an absorption edge near 325 nm and an optical band gap of 3.67 eV and electrical properties covering an electrical resistivity of 5.27 × 10⁻⁴ Ω cm and a carrier concentration of 1.11 × 10²¹ cm⁻³ with a Hall mobility of 10.7 cm²/V s.