Single-Crystal Bismuth Thiophosphate, BiPS₄, as a Nontoxic and Mechanically Robust X-ray Detector

Bismuth thiophosphate, BiPS4, is a promising nontoxic, high-density ternary chalcogenide semiconductor. Polycrystalline BiPS4 was synthesized from the stoichiometric melt of Bi, P, and S. Phosphorus was purified via an in-situ sublimation method. Single crystals of BiPS4 were grown using a modified vertical Bridgman method with a thermal gradient of 18 °C/cm. The material exhibits an electrical resistivity of 2 × 109 Ω·cm. The Knoop hardness of the single crystals is 128 ± 0.8 kg mm–2. A blocking contact behavior was observed with asymmetric contacts of Ga/BiPS4/Ag. A clear photocurrent response was observed from a BiPS4 crystal under an electric field as low as 1.14 V mm–1. Using a tungsten X-ray source, an X-ray sensitivity of 52 μ Gy–1 cm–2 was measured under an electric field of 80 V mm–1. When a single-crystal BiPS4 radiation detector device was used in a pulse-height radiation detection system, a clear charge collection response was observed under a 241Am α-particle radiation source.