Mercury Chalcohalide Semiconductor Hg₃Se₂Br₂ for Hard Radiation Detection

Hg₃Se₂Br₂ is a wide band gap semiconductor (2.22 eV) with high density (7.598 g/cm³) and crystallizes in the monoclinic space group C2/m with cell parameters of a = 17.496 (4) Å, b = 9.3991 (19) Å, c = 9.776(2) Å, β = 90.46(3)°, V = 1607.6(6) ų. It melts congruently at a low temperature, 566 °C, which allows for an easy single crystal growth directly from the stoichiometric melt. Single crystals of Hg₃Se₂Br₂ up to 1 cm long have been grown using the Bridgman method. Hg₃Se₂Br₂ single crystals exhibit a strong photocurrent response when exposed to Ag X-ray and blue diode laser. The resistivity of Hg₃Se₂Br₂ measured by the two probe method is on the order of 10¹¹ cm, and the mobility-lifetime product (μτ) of the electron and hole carriers estimated from the energy spectroscopy under Ag X-ray radiation are (μτ)_e ≈ 1.4 × 10^-4 cm²/V and (μτ)_h ≈ 9.2 × 10^-5 cm²/V. Electronic structure calculations at the density functional theory level indicate a direct band gap and a relatively small effective mass for carriers. On the basis of the photoconductivity and hard X-ray spectrum, Hg₃Se₂Br₂ is a promising candidate for X-ray and γ-ray radiation detection at room temperature.