Browsing by Author "Djamel, Allali"

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    Electronic and Optical Properties of the Spinel Oxides GeB2O4 (B = Mg, Zn and Cd): An Ab-Initio Study
    (Université de M'sila, 2019) Djamel, Allali
    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.