Cs2Hg3S4: A low-dimensional direct bandgap semiconductor

Saiful M. Islam, S. Vanishri, Hao Li, Constantinos C. Stoumpos, John A. Peters, Maria Sebastian, Zhifu Liu, Shichao Wang, Alyssa S. Haynes, Jino Im, Arthur J. Freeman, Bruce Wessels, Mercouri G. Kanatzidis

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Abstract

Cs2Hg3S4 was synthesized by slowly cooling a melted stoichiometric mixture of Hg and Cs2S4. Cs2Hg3S4 crystallizes in the Ibam spacegroup with a = 6.278(1) Å, b = 11.601(2) Å, and c = 14.431(3)Å; dcalc = 6.29 g/cm3. Its crystal structure consists of straight chains of [Hg3S4]n2n- that engage in side-by-side weak bonding interactions forming layers and are charge balanced by Cs+ cations. The thermal stability of this compound was investigated with differential thermal analysis and temperature dependent in situ synchrotron powder diffraction. The thermal expansion coefficients of the a, b, and c axes were assessed at 1.56 × 10-5, 2.79 × 10-5, and 3.04 × 10-5 K-1, respectively. Large single-crystals up to ∼5 cm in length and ∼1 cm in diameter were grown using a vertical Bridgman method. Electrical conductivity and photoconductivity measurements on naturally cleaved crystals of Cs2Hg3S4 gave resistivity ρ of ≥108 ω·cm and carrier mobility-lifetime (μδ) products of 4.2 × 10-4 and 5.82 × 10-5 cm2 V-1 for electrons and holes, respectively. Cs2Hg3S4 is a semiconductor with a bandgap Eg ∼ 2.8 eV and exhibits photoluminescence (PL) at low temperature. Electronic band structure calculations within the density functional theory (DFT) framework employing the nonlocal hybrid functional within Heyd-Scuseria-Ernzerhof (HSE) formalism indicate a direct bandgap of 2.81 eV at. The theoretical calculations show that the conduction band minimum has a highly dispersive and relatively isotropic mercury-based s-orbital-like character while the valence band maximum features a much less dispersive and more anisotropic sulfur orbital-based band.

Original languageEnglish
Pages (from-to)370-378
Number of pages9
JournalChemistry of Materials
Volume27
Issue number1
DOIs
Publication statusPublished - Jan 13 2015

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ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

Cite this

Islam, S. M., Vanishri, S., Li, H., Stoumpos, C. C., Peters, J. A., Sebastian, M., Liu, Z., Wang, S., Haynes, A. S., Im, J., Freeman, A. J., Wessels, B., & Kanatzidis, M. G. (2015). Cs2Hg3S4: A low-dimensional direct bandgap semiconductor. Chemistry of Materials, 27(1), 370-378. https://doi.org/10.1021/cm504089r