Optical and electronic properties of post-annealed ZnO:Al thin films

This study examined the optical and electronic properties of post-annealed Al-doped ZnO (ZnO:Al) thin films. The lowest resistivity was observed after annealing a sputter-deposited ZnO:Al film at 350 °C. X-ray photoelectron spectroscopy revealed a ∼0.4 eV shift in the Fermi level when the carrier concentration was increased to 1.6×1020 cm−3 by Al doping and annealing. The optical band gap increased from 3.2 eV for insulating ZnO to 3.4 eV for conducting ZnO:Al, and was associated with conduction-band filling up to ∼0.4 eV in a renormalized band gap. Schematic band diagrams are shown for the ZnO and ZnO:Al films.