Effect of li-doping on photoluminescence of screen-printed zinc oxide films

Undoped and Li-doped ZnO films were fabricated by screen printing approach on sapphire substrate. The effect of Li doping and annealing temperature on the luminescent, optical, electrical and structural properties of the films has been investigated by the photoluminescence (PL), Raman scattering, conductivity, Atomic Force microscopy and X-ray diffraction (XRD) methods. The XRD study revealed that the films have polycrystalline wurtzite structure with grain sizes ranging from 26 to 38 nm. In the undoped ZnO films, the increase of annealing temperature from 800 to 1000°C resulted in the increase of the grain sizes, film conductivity and the intensity of the ultraviolet PL. The introduction of Li of low concentration of 0.003 wt % at 800°C or 900°C allows producing the low-resistive films with enhanced ultraviolet PL and reduced density of crystalline defects. Highly doped films (with 0.3 wt % of Li) were found to be semi-insulating with deteriorated PL properties irrespectively of the annealing temperature. It is shown that introduction of Li in the ZnO films affects their PL spectra mainly via the evolution of the film crystallinity and the density of intrinsic defects.