CsHgInS₃: A new quaternary semiconductor for γray detection

The new layered compound CsHgInS₃ was synthesized using solid state and flux synthesis techniques. The compound is a semiconductor and shows promising properties for X-ray and γray detection. It features a layered structure that crystallizes in the monoclinic space group C2/c with cell parameters: a = 11.2499(7) Å, b = 11.2565(6) Å, c = 22.146(1) Å, β = 97.30(5)°, V = 2781.8(4) ų, and Z = 8. CsHgInS₃ is isostructural to Rb₂Cu₂Sn ₂S₆, where the Hg, In, and Cs atoms occupy the Cu, Sn, and Rb sites, respectively. Large single crystals with dimension up to 5 mm were grown with a vertical Bridgman method as well as a horizontal traveling heater method. CsHgInS₃ has a γray attenuation length comparable to commercial Cd_1-xZn_xTe and a band gap value of 2.30 eV. The electrical resistivity of CsHgInS₃ is anisotropic with values of 98 Gω cm and 0.33 Gω cm perpendicular and parallel to the (001) plane, respectively. The mobility-lifetime product (μτ) of electrons and holes estimated from photoconductivity measurements on the as-grown crystals were (μτ)_e = 3.6 × 10^-5 cm² V ^-1 and (μτ)_h = 2.9 × 10^-5 cm ² V^-1, respectively. Electronic structure calculations at the Density Functional Theory level were performed based on the refined crystal structure of CsHgInS₃ and show a direct gap with the conduction band near the Fermi level being highly dispersive, suggesting a relatively small carrier effective mass for electrons.