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.
This paper aims to compile the low carbon strategies adopted in all levels of schools through the methods of literature review, experts consulting and questionnaire survey. The general survey of Taipei City campuses comes to the conclusions that the aspects of "Management of Energy and Resource", "Learning, Publicizing and Further Education" and "Energy-saving of Building and Environment" are the main strategies adopted, and understand the different choices of strategies between all levels of schools.
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