Investigation of Semi-Insulating Cs₂Hg₆S₇ and Cs₂Hg_6‑xCd_<i>x</i>S₇ Alloy for Hard Radiation Detection

A new method is described to synthesize the semiconductor Cs2Hg6S7 and its alloy with Cd. Using the as-synthesized material, large single crystals have been grown by the Bridgman method under an improved set of crystal growth parameters. In addition, Cd alloying in the form of Cs2Hg6–xCdxS7 (x = 0.25, 0.5, 0.75, etc.) as well as doping with In, Cl was investigated and the influence on the electronic properties was studied. Cd alloying increases the band gap of Cs2Hg6S7 from 1.63 to 1.84 eV. Doping with In and Cl however creates electron carriers and changes p-type samples of Cs2Hg6S7 into n type. A 30-fold increase in the resistivity of the single crystals from 2 × 106 to 0.65 × 108 Ω cm has been achieved. The carrier mobility-lifetime product of the Cs2Hg6S7 crystals has been increased to 1.7 × 10–3 cm2/V for electrons (μτ)e and 2.4 × 10–3 cm2/V for holes (μτ)h (HgCl2 doped). The measured (μτ)e value is comparable to the commercial CdZnTe crystal while the (μτ)h is 10 times higher. Detection of Ag X-ray radiation is demonstrated using the as-grown Cs2Hg6S7 crystals.