BiI₃ single crystal for room-temperature gamma ray detectors

BiI₃ single crystals were grown by the physical vapor transport method. The repeated sublimation of the starting material reduced impurities in the BiI₃ single crystal to sub-ppm levels. The detector was fabricated by depositing Au electrodes on both surfaces of the 100-μm-thick BiI₃ single crystal platelet. The resistivity of the BiI₃ single crystal was increased by post-annealing in an iodine atmosphere (ρ=1.6×10¹¹ Ω cm). Pulse height spectroscopy measurements showed clear peaks in the energy spectrum of alpha particles or gamma rays. It was estimated that the mobility-lifetime product was μ_eτ_e=3.4-8.5×10^-6 cm²/V and the electron-hole pair creation energy was 5.8 eV. Our results show that BiI₃ single crystals are promising candidates for detectors used in radiographic imaging or gamma ray spectroscopy.