Investigation of electronic and optical properties in Al−Ga codoped ZnO thin films

Electronic and optical properties of Al−Ga codoped ZnO thin films were investigated by post-annealing. The lowest resistivity of the Al–Ga codoped ZnO films was observed from the 450 °C-annealed sample. The Fermi-level shift of the Al−Ga codoped ZnO film was ∼0.6 eV from x-ray photoelectron spectroscopy, and the widening of optical-bandgap in the Al−Ga codoped ZnO film was ∼0.3 eV. The correlations of optical-bandgap with Fermi-level shift and conduction band filling were suggested by schematic band diagrams. ► The Fermi-level shift of 450 °C-annealed ZnO:(Al,Ga) film is ∼0.6 eV compared to ZnO. ► The widening of optical-bandgap energy is ∼0.3 eV. ► Conduction band filling obtained from the carrier concentration is ∼0.45 eV. ► Optical-bandgap is correlated with the Fermi-level shift and conduction band filling.