Layered BiOI single crystals capable of detecting low dose rates of X-rays
Robert A. Jagt, Ivona Bravić, Lissa Eyre, Krzysztof Gal̷kowski, Joanna Borowiec, Kavya Reddy Dudipala, Michał Baranowski, Mateusz Dyksik, Tim W. J. van de Goor, Theo Kreouzis, Ming Xiao, A. J. Bevan, Paulina Płochocka, Samuel D. Stranks, Felix Deschler, Bartomeu Monserrat, Judith L. MacManus‐Driscoll, Robert L. Z. Hoye
Abstract
Abstract Detecting low dose rates of X-rays is critical for making safer radiology instruments, but is limited by the absorber materials available. Here, we develop bismuth oxyiodide (BiOI) single crystals into effective X-ray detectors. BiOI features complex lattice dynamics, owing to the ionic character of the lattice and weak van der Waals interactions between layers. Through use of ultrafast spectroscopy, first-principles computations and detailed optical and structural characterisation, we show that photoexcited charge-carriers in BiOI couple to intralayer breathing phonon modes, forming large polarons, thus enabling longer drift lengths for the photoexcited carriers than would be expected if self-trapping occurred. This, combined with the low and stable dark currents and high linear X-ray attenuation coefficients, leads to strong detector performance. High sensitivities reaching 1.1 × 10 3 μC Gy air −1 cm −2 are achieved, and the lowest dose rate directly measured by the detectors was 22 nGy air s −1 . The photophysical principles discussed herein offer new design avenues for novel materials with heavy elements and low-dimensional electronic structures for (opto)electronic applications.