Title:Study of Electronic Band Structure and Optical Properties Al-F co-doped ZnO
VOLUME: 14 ISSUE: 6
Author(s):Lixin Wang, Xiaopeng Zhu, Lei Bai, Lin Lu, Yao Li and Xiujuan Qin*
Affiliation:Hebei Key Laboratory of Applied Chemistry, Yanshan University, 438 HebeiStreet, Qinhuangdao 066004, Hebei, Hebei Key Laboratory of Applied Chemistry, Yanshan University, 438 HebeiStreet, Qinhuangdao 066004, Hebei, Hebei Key Laboratory of Applied Chemistry, Yanshan University, 438 HebeiStreet, Qinhuangdao 066004, Hebei, Hebei Key Laboratory of Applied Chemistry, Yanshan University, 438 HebeiStreet, Qinhuangdao 066004, Hebei, Hebei Key Laboratory of Applied Chemistry, Yanshan University, 438 HebeiStreet, Qinhuangdao 066004, Hebei, Hebei Key Laboratory of Applied Chemistry, Yanshan University, 438 HebeiStreet, Qinhuangdao 066004, Hebei
Keywords:Al-F co-doped ZnO, first principles, fermi level, electronic band structure, optical properties, thin film.
Abstract: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.
