CsHgInS₃: a New Quaternary Semiconductor for γ-ray Detection

The new layered compound CsHgInS 3 was synthesized using solid state and flux synthesis techniques. The compound is a semiconductor and shows promising properties for X-ray and γ-ray detection. It features a layered structure that crystallizes in the monoclinic space group C 2/ c with cell parameters: a = 11.2499(7) Ǻ, b = 11.2565(6) Ǻ, c = 22.146(1) Ǻ, β = 97.30(5)°, V = 2781.8(4) Ǻ 3, and Z = 8. CsHgInS 3 is isostructural to Rb 2 Cu 2 Sn 2 S 6, 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. CsHgInS 3 has a γ-ray attenuation length comparable to commercial Cd 1– x Zn x Te and a band gap value of 2.30 eV. The electrical resistivity of CsHgInS 3 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 cm 2 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 CsHgInS 3 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.