Band gap of Hg chalcogenides: Symmetry-reduction-induced band-gap opening of materials with inverted band structures

We have investigated the band structure of zinc-blende (ZB) Hg chalcogenides using a corrected local density approximation method. We find that the band gaps of HgS, HgSe, and HgTe are 0.30, -0.24, and -0.31 eV, respectively. That is, HgS has a positive band gap, whereas HgSe and HgTe have inverted band structures. The chemical trend of the band gaps is explained by the atomic energy levels and sizes, as well as by the related deformation potentials for these compounds. We also show systematically how the band gap of the inverted band structure can open up when the T-d symmetry of the ZB structure is reduced under strain or in the presence of a surface or interface.