Surface States in Negative-Band-Gap Semiconductor Films: Intrinsic or Topological?
Natalia Malkova, Garnett W. Bryant
Recently surface states in negative gap structures made of semiconductors like HgTe, which appear due to the band structure inversion, have attracted renewed interest because of their possible topological origin. We investigate the origin of surface states in HgTe films. The electronic band structure of three types of  HgTe slabs, that differ by the terminating surface layers, are studied using the tight-binding approach. Surface layers of slabs are passivated to remove dangling bonds. We show that surface states evolve from the cation derived dangling-back bond band, and that they must be classified as intrinsic surface states to the inverted gap materials. These surface states are sensitive both to the type of the surface layer and to the passivating potential. The surface states can be formed only when the passivating potential reaches a threshold value needed to overlap the positive band gap of the surface layers and negative band gap of the interior layers of the slabs. The surface states found do not have any characteristic topological properties: they are not gapless, they also cannot prevent back-scattering required for dissipation-less transport.