Background: Al-F co-doped ZnO systems are investigated by the first principles calculations.
Synchronously, we successfully prepared Al-F co-doped ZnO thin films using the aerosolassisted
chemical vapor deposition technique. The computational results reveal that the Fermi energy
of the Al-F co-doped ZnO system shifts to the conduction band in the electronic band structure,
which illustrates that the Al-F co-doped ZnO system is an n-type semiconductor. Furthermore, Al-F
co-doped ZnO system has much smaller minimum band gap than pure ZnO system and Al, F monodoped
ZnO systems, which indicates its better conductive performance. Experimental results confirm
the Al-F co-doping ZnO thin film has the smallest sheet resistance. More importantly, for the optical
properties, the strong absorption of Al mono-doped and F mono-doped ZnO systems occurs in the
UV region, while the obvious absorption of Al-F co-doped ZnO system happens in the visible-light
region. Experimental results of photoluminescence spectroscopy can confirm the conclusion. These
results suggest that Al-F co-doped ZnO system has excellent electrical conductivity and optical properties.
Objective: Our work mainly concentrates on the Al-F co-doping ZnO system and its electronic band
structure and optical properties in terms of experimental studies and theoretical calculations simultaneously.
Methods: The ultrasoft pseudopotentials and CASTEP code of plane wave are used to execute all
calculations, and depositing ZnO thin films on a glass substrate used by a cold wall aerosol assisted
chemical vapor deposition method.
Results: We use first principles and experimental results to study ZnO:Al, ZnO:F and ZnO:Al-F
systems. We found that F and Al co-doped ZnO thin films resulted in the decrease of both the resistivity
and the optical absorption in the visible range compared with the mono-doping systems
(ZnO:Al, ZnO:F). It indicates that the Al-F co-doping ZnO system shows better conductive and optical
performances in the visible light range.
Conclusion: In summary, first principles calculations and experimental results have been performed
to study the electronic band structure and optical properties of the ZnO:Al-F system. The electronic
band structures show that ZnO:Al-F system exhibits n-type semiconductor, whereas the Fermi level
shifts to the conduction band and exhibits metal-like characteristics with Al-F co-doping. The calculated
optical properties indicate that the optical energy gap increases with Al-F co-doping. More
importantly, a strong absorption in the visible-light region has been found with Al-F co-doping,
which originates mainly from the transition between F 2p and Al 3p states. Our calculations provide
electronic structure evidence that, in addition to the usage as optoelectronic devices, the ZnO:Al-F
system could be a potential candidate for photo-electrochemical application due to the nature of the
activity in the visible-light region.