First principles calculations and experimental study of the optical properties of Ni-doped ZnS

Zinc sulphide doped with nickel (Ni:ZnS) has many applications in different fields like materials science, electronics, optics, and other industrial applications. Experimentally, a large variety of methods have been developed for Ni:ZnS synthesizing, where the chemical synthesis with capping agent is most successful, but has disadvantages like purity and the low performance. In addition, since there is not also much theoretical information about its features, the electronic and optical response of Ni:ZnS were studied, both experimentally by x-ray diffractometry (XRD), transmission electron microscopy (HR-TEM), and x-ray photoelectron spectroscopy (XPS) and theoretically by means of the density functional theory (DFT) calculations, giving an unified understanding of the electrooptical performance of this compound. In the same way, the importance of the inclusion of Ni impurities in the structure was studied and analyzed by the inclusion of a Hubbard potential in the calculations. We found that the optimal U value for Ni atoms is 4 eV in agreement with experimental results obtained by XPS. The dielectric function (ϵ ₂) for pure and doped systems showed that the influence of the Ni atom is mainly given in the range of low energy regions (E < 6 eV), where the new peaks are associated to transitions that include the impurity band states.