Optical and electronic anisotropies in perovskitoid crystals of Cs3Bi2I9 studies of nuclear radiation detection

The halide perovskitoid compound Cs3Bi2I9 (CBI) has attracted considerable interest as a semiconductor because of its outstanding stability and reduced toxicity compared with lead-based halide perovskites. Here, we report the growth of nuclear radiation detection grade CBI bulk crystals (phi 15 x 60 mm(3)) with a high resistivity of over 10(10) cm using a modified vertical Bridgman method. Because of their layered crystal structures we investigated the anisotropy in the optical and electrical properties using different crystal orientations. The CBI(001) sample exhibits a resistivity of approximate to 10(12) cm compared to approximate to 10(10) cm for the CBI(100) sample. This is due to the anisotropic mobility in the two crystallographic directions. Using 425 nm LED (approximate to 200 mW cm(-2)) illumination CBI(001) possesses a superior optical response with a switching ratio of over 40, which is critically higher than that of CBI(100) (<2). Detectors of 2 mm thickness show a capability of detecting Am-241@5.49 MeV particles, with good peak discrimination. A full width at half maximum (FWHM) of 32% was obtained under a bias of 560 V. Simultaneously, the electron mobility and mobility lifetime () were calculated to be 6.10 cm(2) V-1 s(-1) and 2.03 x 10(-5) cm V-1, respectively. First-principles density functional theory calculations confirm the crystallographic anisotropy of the carrier effective masses. In addition, a significant X-ray sensitivity of 111.9 C Gy(-1) cm(-2) for a CBI detector was observed, under 80 kVp X-rays at an electrical field of 450 V cm(-1).