Photoconductivity in Tl6SI4: A Novel Semiconductor for Hard Radiation Detection

The chemical concept of lattice hybridization was applied to identify new chalcohalide compounds as candidates for X-ray and γ-ray detection. Per this approach, compound semiconductor materials with high density and wide band gaps can be produced that can absorb and detect hard radiation. Here, we show that the mixed chalcogenide–halide compound Tl 6 SI 4 is a congruently melting, mechanically robust chalcohalide material with strong photoconductivity response and an impressive room-temperature figure of merit. Tl 6 SI 4 crystallizes in the tetragonal P 4/ mnc space group, with a = 9.1758(13) Å, c = 9.5879(19) Å, V = 807.3(2) Å 3, and a calculated density of 7.265 g·cm –3 . The new material requires a more simplified crystal growth compared to the leading system Cd 0.9 Zn 0.1 Te, which is the benchmark room-temperature hard radiation detector material. We successfully synthesized Tl 6 SI 4 crystals to produce detector-grade wafers with high resistivity values (∼10 10 Ω·cm) and high-resolution detection of X-ray spectra from an Ag (22 keV) source.