On the electrical conductivity in Al:ZnO layers; experimental investigation and a theoretical approach

Multi-layered Al:ZnO thin films, with wurtzite - type structure and thickness up to 120 nm, as determined by x-ray diffraction and HRTEM, were grown on Si-SiO₂ and glass substrates by the sol-gel method. Fluorescence spectroscopy measurements show that 0.5 at.% Al doping determines a blue shift of the emission band observed at 387nm in the undoped material. The room temperature conductivity increases when the number of layers increases, to reach a value of 3.70 (Ω·m)^-1 for a ten layer film. Results obtained by total energy first principles calculations performed on systems with chemical disorder are discussed in relationship with experimental data to account for the effect of Al on the conductivity.