First-principles calculation of the structural, electronic and optical properties of GaSe_(1-x) S_(x) (x = 0, 0.25, 0.5 and 1) compounds

Abstract

ABSTRACT The industry has long sought ever more efficient materials, allowing it to meet market demand. For this purpose, doping remains a good choice for improving the properties of a material. The structural, electronic, optical properties of the (x = 0, 0.25, 0.5 and 1) compounds are studied using the pseudopotential method of first principles in the Density Functional Theory using CASTEP code. The calculated results show that the lattice constants of ε-GaSe decrease as function of the impurity concentration increases. Also, the increase of doping by the sulphur leads to a decrease of and an increase of . The values of the gap energy are increased with the increase in sulphur content. For optical calculations the results show the appearance of an absorption peak in all (x = 0, 0.25, 0.5 and 1) structures, with different intensities and a shift of the band to lower wavelengths when the doping content by the sulphur is increased. The insertion of the sulphur atom reduces the refractive index of ε-GaSe, and increases its birefringence which is important for non-linear optics applications. Raman lines move to higher frequencies with increasing sulphur content indicating a change in the crystal structure of ε-GaSe.