Electronic and Optical Properties of the Spinel Oxides GeB2O4 (B = Mg, Zn and Cd): An Ab-Initio Study
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Date
2019
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Université de M'sila
Abstract
We report ab-initio density functional theory calculations of the electronic and optical properties of the spinel
oxides GeMg2O4, GeZng2O4 and GeCd2O4 using the full potential linearized augmented plane-wave method.
To calculate the electronic properties, the exchange-correlation interaction was treated with various functionals.
We find that the newly developed Tran–Blaha modified Becke–Johnson functional significantly improves
the band gap value. All considered GeB2O4 compounds are direct band gap materials. The band gap value
decreases with increasing atomic size of the B element. The decrease of the fundamental direct band gap
( – ) when one moves from GeMg2O4 to GeZn2O4 to GeCd2O4 can be attributed to the p–d mixing in the
upper valence bands of GeZn2O4 and GeCd2O4. The lowest conduction band, which is mainly originated from
the s and p states of the Ge and B (B = Mg, Zn, Cd) atoms, is well dispersive, similar to that of transparent
conducting oxides such as ZnO. The topmost valence band, which is originated from the O-2p and B-d states,
is considerably less dispersive. Optical spectra in a wide energy range from 0 to 30 eV are provided and
the origin of the observed peaks and structures are assigned. We find that the zero-frequency limit of the
dielectric function (0) increases with decreasing band gap value.
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Keywords
Semiconductor, Ab Initio Calculation, Optical Properties, Electronic Structure