Crystal Growth and Characterization of the X-ray and gamma-ray Detector Material Cs2Hg6S7

Abstract

Cs2Hg6S7 is a promising compound for X-ray and gamma-ray detection with a band gap of 1.63 eV. A new method is reported for the synthesis of Cs2Hg6S7, along with growth studies of large Cs2Hg6S7 crystals of dimensions up to several centimeters using the Bridgman method. Our growth technique gives reproducible crystals with high resistivity (10(6) ohm center dot cm). Crystals grown in this work exhibit figure of merit mobility lifetime (mu tau) products comparable to commercial cadmium zinc telluride (CZT). The Cs2Hg6S7 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 Cs2Hg6S7 crystals is discussed. The noncentrosymmetric character of the tetragonal crystal structure (space group P4(2)nm) gives rise to a nonlinear optical second harmonic generation response.