Crystal growth and characterization of the X-ray and γ-ray detector material Cs ₂Hg ₆S ₇

Cs ₂Hg ₆S ₇ is a promising compound for X-ray and γ-ray detection with a band gap of 1.63 eV. A new method is reported for the synthesis of Cs ₂Hg ₆S ₇, along with growth studies of large Cs ₂Hg ₆S ₇ crystals of dimensions up to several centimeters using the Bridgman method. Our growth technique gives reproducible crystals with high resistivity (10 ⁶ ohm•cm). Crystals grown in this work exhibit figure of merit mobility lifetime (μτ) products comparable to commercial cadmium zinc telluride (CZT). The Cs ₂Hg ₆S ₇ crystals exhibit a strong photoluminescence signal at low temperature in the range 1.50-1.75 eV. The thermal properties of the crystal, including the thermal expansion coefficient and the thermal conductivity, have been characterized. The nature of defects affecting the charge transport properties in the as-grown Cs ₂Hg ₆S ₇ crystals is discussed. The noncentrosymmetric character of the tetragonal crystal structure (space group P4 ₂nm) gives rise to a nonlinear optical second harmonic generation response.