Elaboration and characterization of Al doped ZnO nanorod thin films annealed in hydrogen

Research highlights: → High transparent and conductive Al doped ZnO nanorod thin films were synthesized using sol-gel spin-coating method. → Al doped ZnO nanorod thin films can be got by annealing in hydrogen rather than in air. → Crystal orientation of Al doped ZnO thin film has been raised. → Resistivity of films has been remarkably reduced by annealing in hydrogen. - Abstract: ZnO thin films doped with Al concentrations of 1.0, 2.0, 3.0, 4.0, 5.0 at% were prepared by a sol-gel spin-coating method on glass substrates and respectively annealed at 550 deg. C for 2 h in hydrogen and air. The X-ray diffraction and selected-area electron diffraction results confirm that the Al doped ZnO thin films are of wurtzite hexagonal ZnO. The scanning electron microscope results indicate that the Al doped ZnO nanorod thin films can be got by annealing in hydrogen rather than in air. The optical properties reveal that the Al doped ZnO thin films have obviously enhanced transmittance in the visible region. The electrical properties show that the resistivity of 1.0 at% Al doped ZnO thin films has been remarkably reduced from 0.73 Ω m by annealing in air to 3.2 x 10-5 Ω m by annealing in hydrogen. It is originated that the Al doped ZnO nanorod thin films annealed in hydrogen increased in electron concentration and mobility due to the elimination of adsorbed oxygen species, and multicoordinated hydrogen.