Vacancy defects transform zinc tellurite glass from insulator to semiconductor: A first-principles prediction

Abstract

The effect of vacancy defects on the zinc tellurite glass (ZnTeO3) was investigated by performing density functional theory using GGA-PBESOL functional and norm-conserving pseudopotential. The effect of the inclusion of Hubbard-U correction for only Ud, Zn state or Up, O state or both states was investigated to obtain the experimental band gap. The lattice parameters, band structure, and density of states of ZnTeO3 were predicted. The value of Up, O has a significant impact on the band gap (Egap) value of ZnTeO3. Our calculated Egap exactly agrees with the experimental value (4.1 eV). The Egap values of the vacancies were significantly decreased as compared to the perfect structure. The Egap values of the Zn-vacancy and Te-vacancy were 2.5 eV and 2.0 eV, respectively. Three kinds of O vacancies were studied and their Egap values ranged from 2.2 eV to 2.5 eV. The vacancy defects changed the insulating character of ZnTeO3 to semiconductor behavior, which may have promising applications. The vacancies stability follows the order of perfect crystal > O-vacancy > Zn-vacancy > Te-vacancy, i.e., based on their cohesive energies. The formation energies were calculated and indicated that the spontaneous formation of the vacancies is impossible; however, the formation of the O-vacancy was determined to be the most probable, followed by Zn-vacancy and then Te-vacancy under specific conditions. The optical properties (refractive index, reflectivity, dielectric function, optical conductivity, and loss function) and thermodynamic properties of zinc ZnTeO3 and its vacancy defects were predicted.