Electronic structure of CuCl1-xBrx solid solutions: first-principles calculations in the meta-GGA approximation

The electronic structure of CuCl and CuBr compounds and their solid solutions CuCl1–xBrx (x = 0.25, 0.50, 0.75) has been calculated in the framework of the density functional theory. The calculations have been performed in the basis of pseudoatomic orbitals using the simple local approximation (LDA) and the new meta-GGA exchange potential TB09, which, to a large extent, compensates the LDA error in the description of the position of conduction bands in semiconductors. A comparative analysis of the main characteristics of the electronic structure of binary compounds and their solutions has been carried out. It has been found that the composition dependence of the band gap Eg(x) has a small downward bowing with the coefficient b ~ 0.09 eV

Ab initio calculations of optical constants of GaSe and InSe layered crystals

The dielectric functions, refractive indices, and extinction coefficients of GaSe and InSe layered crystals have been calculated within the density functional theory. The calculations have been performed for the values of theoretical structural parameters optimized using the exchange-correlation functional, which allows one to take into account the dispersion interactions. It has been found that optical functions are characterized by the most pronounced polarization anisotropy in the range of photon energies of ∼4–7 eV. The frequency dependences for InSe compound in the range up to 4 eV demonstrate the more pronounced anisotropy as compared to GaSe. The results obtained for GaSe crystal agree better with the experimental data as compared to the previous calculations

Influence of size effects on the electronic structure of hexagonal gallium telluride

Using methods of the density functional theory, the electronic band structure of a hexagonal modification of the layered GaTe semiconductor has been calculated. The structural parameters of a bulk crystal with the β-polytype symmetry have been determined taking into account van der Waals interactions and agree with experimental data for polycrystalline films within 2%. Estimates for the position of extrema of the upper valence band and the lower conduction band have been obtained with respect to the vacuum level for bulk β-GaTe and for ultrathin plates with the number of elementary layers ranging from 1 to 10, which corresponds to a thickness range of 0.5–8 nm. The calculations demonstrate that hexagonal GaTe is an indirect band gap semiconductor with a forbidden band width varying from 0.8 eV in the bulk material to 2.3 eV in the monolayer