Defect Antiperovskite Compounds Hg₃Q₂I₂ (Q = S, Se, and Te) for Room-Temperature Hard Radiation Detection

The high Z chalcohalides Hg₃Q₂I₂ (Q = S, Se, and Te) can be regarded as of antiperovskite structure with ordered vacancies and are demonstrated to be very promising candidates for X- and γ-ray semiconductor detectors. Depending on Q, the ordering of the Hg vacancies in these defect antiperovskites varies and yields a rich family of distinct crystal structures ranging from zero-dimensional to three-dimensional, with a dramatic effect on the properties of each compound. All three Hg₃Q₂I₂ compounds show very suitable optical, electrical, and good mechanical properties required for radiation detection at room temperature. These compounds possess a high density (>7 g/cm³) and wide bandgaps (>1.9 eV), showing great stopping power for hard radiation and high intrinsic electrical resistivity, over 10¹¹ Ω cm. Large single crystals are grown using the vapor transport method, and each material shows excellent photo sensitivity under energetic photons. Detectors made from thin Hg₃Q₂I₂ crystals show reasonable response under a series of radiation sources, including ²⁴¹Am and ⁵⁷Co radiation. The dimensionality of Hg-Q motifs (in terms of ordering patterns of Hg vacancies) has a strong influence on the conduction band structure, which gives the quasi one-dimensional Hg₃Se₂I₂ a more prominently dispersive conduction band structure and leads to a low electron effective mass (0.20 m₀). For Hg₃Se₂I₂ detectors, spectroscopic resolution is achieved for both ²⁴¹Am α particles (5.49 MeV) and ²⁴¹Am γ-rays (59.5 keV), with full widths at half-maximum (FWHM, in percentage) of 19% and 50%, respectively. The carrier mobility-lifetime μτ product for Hg₃Q₂I₂ detectors is achieved as 10^-5-10^-6 cm²/V. The electron mobility for Hg₃Se₂I₂ is estimated as 104 ± 12 cm²/(V·s). On the basis of these results, Hg₃Se₂I₂ is the most promising for room-temperature radiation detection.