Theoretical investigations of the effect of vacancies on the geometric and electronic structures of zinc sulfide

The effects of S-vacancy and Zn-vacancy on the geometric and electronic structures of zinc blende ZnS are investigated by the first-principles calculation of the plane wave ultrasoft pseudopotential method based on the density functional theory. The results demonstrate that both S-vacancy and Zn-vacancy decrease the cell volume and induce slight deformation of the perfect ZnS. Furthermore, this change of geometric structure caused by Zn-vacancy is more obvious than the one due to the S-vacancy. The formation energy of S-vacancy is higher than that of Zn-vacancy, indicating that Zn-vacancy is easier to form than S-vacancy in ZnS crystal. Electronic structure analysis shows that Zn-vacancy increases the band-gap of ZnS from 2.03 eV to 2.15 eV, while the S-vacancy has almost no effect on the band-gap of ZnS. Bond population analysis shows that Zn-vacancy increases covalence character of the Zn-S bonds around Zn-vacancy, while S-vacancy shows a relatively weak effect on the covalence character of Zn-S bonds.