TlHgInS₃: An Indirect-Band-Gap Semiconductor with X‑ray Photoconductivity Response

The quaternary compound TlHgInS₃ crystallizes in a new structure type of space group, <i>C</i>2/<i>c</i>, with cell parameters <i>a</i> = 13.916(3) Å, <i>b</i> = 3.9132(8) Å, <i>c</i> = 21.403(4) Å, β = 104.16(3)°, <i>V</i> = 1130.1(8) ų, and ρ = 7.241 g/cm³. The structure is a unique three-dimensional framework with parallel tunnels, which is formed by _∞¹[InS₃^3–] infinite chains bridged by linearly coordinated Hg²⁺ ions. TlHgInS₃ is a semiconductor with a band gap of 1.74 eV and a resistivity of ∼4.32 GΩ cm. TlHgInS₃ single crystals exhibit photocurrent response when exposed to Ag X-rays. The mobility-lifetime product (μ<i>τ</i>) of the electrons and holes estimated from the photocurrent measurements are (<i>μτ</i>)_e ≈ 3.6 × 10^–4 cm²/V and (<i>μτ</i>)_h ≈ 2.0 × 10^–4 cm²/V. Electronic structure calculations at the density functional theory level indicate an indirect band gap and a relatively small effective mass for both electrons and holes. Based on the photoconductivity data, TlHgInS₃ is a potential material for radiation detection applications