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

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.

Experimental and ab initio study of the structural and optical properties of ZnO coatings: Performance of the DFT+U approach

“…7b). Our predictions for all these optical properties are in good agreement with previous calculations by other DFT methods [20,26,31,33,55], as well as with the experimental measurements obtained Figure 8. DFT+U simulated transmittance spectra T in the range of 200-1000 nm for the 2H type ZnO, before and after structural optimization, and comparison with experimental measurement for the Z1 sample for thin films and bulk ZnO possessing the wurtzite phase [8,54].…”

“…In this case, the choice of the U parameter requires detailed studies of its incidence in other properties of ZnO besides E g [24,25,27,30]. Based on its good performance in the pure compound, the DFT+U approach has also been proposed to model the case of ZnO doped with transition metals and lanthanide atoms [28,29,[31][32][33][34][35][36]. So, nowadays, investigations that combine experimental determinations and DFT+U predictions are quite common, because this combination allows a deeper understanding of the materials through the relation of the observed properties and the modelling of their origins [34,[36][37][38][39][40].…”

Understanding near infrared absorption in tin doped indium oxide thin films

“…Additionally, variation in film properties with thickness has also been previously reported [12]. The presence of defect states has been shown to substantially influence the transport properties in the case of ZnO and ITO films [13,14].…”

Highly sensitive CO sensor based on Al-doped-ZnO nanorods-coated resonant microcantilevers

“…In Al-doped ZnO, the population of Al-O bond is higher than that of Zn-O bond. 31) We suggest that, though there is possibility that O atoms also can be replaced by Al atoms, however majority of the Zn atoms in ZnO lattice are replaced by Al atoms 32) and the Zn replaced AZNR lattice structures are energetically more stable. 21) On the basis of free energy calculation, it was predicted that adsorption of CO from its C-head is entropically favorable.…”