Electronic and optical properties of transition metals doped ZnS: first principles study

Electronic and optical properties of TM-doped zinc sulphide (TM=Ti, Co, Ni) were calculated with the FP-LAPW method by using the LSDA and LSDA+U approximations. In this study, we used the cubic structure of ZnS doped with a 6.25% concentration of transition metals. Our computed electronic band structure and density of states show the semiconducting behavior of TM-doped ZnS. We found U=10 eV the adequate value to obtain the filled d-eg states of titanium, and Ti doped ZnS acts as a semiconductor compound. U=3.3 eV applied to Co 3d states gives good results for exchange couplings close to the previous work, and Co doped ZnS shows a semiconducting behavior. U=6.4 eV is applied to nickel 3d states, and Ni doped ZnS keeps its half-metallic character compared to the calculation without Hubbard. In contrast, we used the Jahn Teller effect to break up the Ni-d-t2g level lying around the Fermi level, and Ni doped ZnS changed to semiconductor compound. Furthermore, the optical properties such as the real and imaginary part of dielectric function and the absorption coefficients show new transition peaks after doping ZnS with TM impurity. The energy band gap of ZnS was found to be decreased by doping with transition metal impurity. That tendency agrees well with the available experimental data.