Quantum confinement and quasiparticle corrections in α-HgS from first principles

Abstract

Using a combination of density functional theory and many-body GW corrections, we calculate the quasiparticle band gap of bulk α -HgS and investigate the effect of quantum confinement on the geometric, electronic and optical structures. The basic structural unit of α -HgS is a one-dimensional helical chain consisting of covalently bound Hg and S atoms. When isolated to just a single helix or to a few-helix configuration, we find that α -HgS becomes a wide-gap semiconductor with a quasiparticle band gap as large as 7.0 eV, in contrast to the bulk structure with a direct quasiparticle band gap of 2.8 eV and an indirect gap of 2.14 eV. This dramatic increase in the band gap is attributed to quantum confinement effects on the geometry and intra-helix bonding. Shifts in the band gaps are also reflected as shifts in the low-energy optical absorption spectra calculated via density functional theory. As more helical chains are added, the band gap decreases sharply while the geometry becomes more bulk-like. This work illustrates the strong effects of quantum confinement in low-dimensional α -HgS nanostructures. • Alpha-HgS is an insulating material with one-dimensional symmetry, cleaving only along the crystallographic c-axis. The properties of nanowires built along this direction are explored. • Density functional calculations for nanowires composed of N = 1–6 layers of HgS show a continuously decreasing band gap as the width is increased, attributed to the strong effects of quantum confinement. • First calculation of the GW-corrected band gap in bulk α-HgS, which agrees very well with the experimentally reported value of 2.14 eV and improves upon previously reported values of the DFT band gap. • Optical spectra calculated via density functional theory reflect the changes in the band gaps as the width of the nanowire changes.