Density Functional Theory Studies of Electronic and Optical Properties of ZnS Alloyed with Mn and Cr
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- Institutt for fysikk 
We have presented density functional theory calculations of electronic and optical properties of ZnS, MnS, CrS, and effects of Mn and Cr impurities on electronic properties of pure ZnS using the periodic program BAND. In our calculations, we have used the generalized gradient approximation (GGA) of PW91 to approximate the exchange and correlation energies. The calculated electronic band structure results show that zinc-blende ZnS is a direct band gap material. The calculated electronic band structure and DOS results are in good agreement with previous theoretical and experimental results. Our results indicate that zinc-blende CrS shows a half-metallic behavior, while MnS shows semiconducting behavior. Mn and Cr impurity substitution for Zn result in an expansion of the ZnS crystal structure and creates bulk defect states within the band gap. Mn impurities mainly affect the deep valence bands and the shallow conduction bands of ZnS. Cr impurities mainly affect the shallow and the deep valence bands. Our results for band structure and DOS show that a half-metallic behavior is found in Cr substituted ZnS while semiconducting behavior is found in Mn substituted ZnS. Finally, the frequency dependent dielectric function was calculated to study optical properties. Our results for the dielectric function show that strong and direct absorption at the sharp peak in the spectral region around 6.05 eV is due to a high density of states at the X-point within the Brillouin zone. The calculated results showed intraband absorption in the low frequency region within the band gap, due to Mn and Cr impurity levels.