The mercury chalcohalide, Hg₃Se₂Br₂ is a promising candidate material for X-ray and possibly g-ray radiation detection. It has a very high stopping power, suitable optical band gap, and high resistivity for the detector applications. Large single crystals of Hg₃Se₂Br₂ up to 1 cm in length were grown by the Bridgman method for the first time.

Hg₃Se₂Br₂ crystallizes in a 2D layered structure with [Hg₂Se₂] zigzag chains running parallel to the a-axis weakly bonded by Br atoms (Fig. 1(a)). The resistivity of Hg₃Se₂Br₂ is in the order of 10¹¹ W·cm, and the mobility-lifetime product (m∙t) of the electron and hole carriers estimated from the energy spectroscopy under Ag X-ray radiation are (m∙t)_e ~ 1.4 × 10⁻⁴ cm²/V and (m∙t)_h ~ 9.2 × 10⁻⁵ cm²/V. Pulse height spectra of Ag X-ray were obtained from Hg₃Se₂Br₂ crystal, where the overlapped peaks corresponding to the characteristic lines of Ag K_α 22.2 and K_β 24.9 keV were detected (Fig. 1(c)). The pulse height energy spectra under ⁵⁷Co g-ray Irradiation shows obvious counting compared to the dark condition under positive bias 500, 600, and 700 V, respectively (Fig. 1(d)). 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 low cost and promising material for X-ray and g-ray detection, suggesting that further investigation and development to improve the quality of single crystals are warranted.

“Mercury Chalcohalide Semiconductor Hg₃Se₂Br₂ for Hard Radiation Detection” H. Li, F. Meng, C. D. Malliakas, Z. Liu, D. Y. Chung, B. Wessels, M. G. Kanatzidis Cryst. Growth Des. 2016, 16, 6446–6453 (DOI: 10.1021/acs.cgd.6b01118)