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Materials 2016, 9(8), 647; doi:10.3390/ma9080647

Effects of Al-Impurity Type on Formation Energy, Crystal Structure, Electronic Structure, and Optical Properties of ZnO by Using Density Functional Theory and the Hubbard-U Method

Department of Materials Engineering, Ming Chi University of Technology, New Taipei 24301, Taiwan
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Academic Editor: Lioz Etgar
Received: 9 June 2016 / Revised: 23 July 2016 / Accepted: 27 July 2016 / Published: 1 August 2016
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Abstract

We systematically investigated the effects of Al-impurity type on the formation energy, crystal structure, charge density, electronic structure, and optical properties of ZnO by using density functional theory and the Hubbard-U method. Al-related defects, such as those caused by the substitution of Zn and O atoms by Al atoms (Als(Zn) and Als(O), respectively) and the presence of an interstitial Al atom at the center of a tetrahedron (Ali(tet)) or an octahedron (Ali(oct)), and various Al concentrations were evaluated. The calculated formation energy follows the order Ef(Als(Zn)) < Ef(Ali(tet)) < Ef(Ali(oct)) < Ef(Als(O)). Electronic structure analysis showed that the Als(Zn), Als(O), Ali(tet), and Ali(oct) models follow n-type conduction, and the optical band gaps are higher than that of pure ZnO. The calculated carrier concentrations of the Als(O) and Ali(tet)/Ali(oct) models are higher than that of the Als(Zn) model. However, according to the curvature of the band structure, the occurrence of interstitial Al atoms or the substitution of O atoms by Al atoms results in a high effective mass, possibly reducing the carrier mobility. The average transmittance levels in the visible light and ultraviolet (UV) regions of the Als(Zn) model are higher than those of pure ZnO. However, the presence of an interstitial Al atom within the ZnO crystal reduces transmittance in the visible light region; Als(O) substantially reduces the transmittance in the visible light and UV regions. In addition, the properties of ZnO doped with various Als(Zn) concentrations were analyzed. View Full-Text
Keywords: density functional theory; first-principles calculations; electronic structure; optical property; Al-impurity; ZnO density functional theory; first-principles calculations; electronic structure; optical property; Al-impurity; ZnO
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MDPI and ACS Style

Wu, H.-C.; Chen, H.-H.; Zhu, Y.-R. Effects of Al-Impurity Type on Formation Energy, Crystal Structure, Electronic Structure, and Optical Properties of ZnO by Using Density Functional Theory and the Hubbard-U Method. Materials 2016, 9, 647.

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