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.