CsHgInS3: a New Quaternary Semiconductor for gamma-ray Detection

Abstract

The new layered compound CsHgInS3 was synthesized using solid state and flux synthesis techniques. The compound is a semiconductor and shows promising properties for X-ray and gamma-ray detection. It features a layered structure that crystallizes in the monoclinic space group C2/c with cell parameters: a = 11.2499(7) angstrom, b = 11.2565(6) angstrom, c = 22.146(1) angstrom, beta = 97.30(5)degrees, V= 2781.8(4) angstrom(3), and Z = 8. CsHgInS3 is isostructural to Rb2Cu2Sn2S6, where the Hg, In, and Cs atoms occupy the Cu, Sn, and Rb sites, respectively. Large single crystals with dimension up to 5 mm were grown with a vertical Bridgman method as well as a horizontal traveling heater method. CsHgInS3 has a gamma-ray attenuation length comparable to commercial Cd1-xZnxTe and a band gap value of 2.30 eV. The electrical resistivity of CsHgInS3 is anisotropic with values of 98 G Omega cm and 0.33 G Omega cm perpendicular and parallel to the (001) plane, respectively. The mobility-lifetime product (mu tau) of electrons and holes estimated from photoconductivity measurements on the as-grown crystals were (mu tau)(e) = 3.6 x 10(-5) cm(2) V-1 and (mu tau)(h) = 2.9 x 10(-5) cm(2) V-1, respectively. Electronic structure calculations at the Density Functional Theory level were performed based on the refined crystal structure of CsHgInS3 and show a direct gap with the conduction band near the Fermi level being highly dispersive, suggesting a relatively small carrier effective mass for electrons.