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Role of Stoichiometry in the Growth of Large Pb2P2Se6 Crystals for Nuclear Radiation Detection

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journal contribution
posted on 17.11.2017, 00:00 by Yadong Xu, Xu Fu, Hongjian Zheng, Yihui He, Wenwen Lin, Kyle M. McCall, Zhifu Liu, Sanjib Das, Bruce W. Wessels, Mercouri G. Kanatzidis
Pb2P2Se6 as a heavy element, chemically robust semiconductor, has been identified as a promising material for cost-effective room temperature X/γ-ray detection. Here, we report the properties of Pb2P2Se6 crystals grown by a vertical Bridgman method under off-stoichiometric Se-rich and Pb-rich conditions. Regardless of the conditions the resulting single crystals exhibited high bulk resistivity on the order of 1011 Ω·cm. However, the photoconductivity and charge transport properties varied based on growth condition indicating the different dominant defects associated with the type of stoichiometric deviation. The formation and nature of intrinsic defects in Pb2P2Se6 crystals were also studied by first-principles density functional theory (DFT) calculations as well as thermally stimulated current (TSC) spectroscopy. The TSC results indicated that four traps were common to both Se-rich and Pb-rich Pb2P2Se6, while a higher density of shallow defects were observed in Se-rich Pb2P2Se6. DFT calculations predict that the antisite defects PPb+, PSe and PbP are the dominant deep donors and acceptors in Se-rich and Pb-rich Pb2P2Se6, respectively, which leads to the degradation of mobility lifetime product (μτ) on the order of 10–5 cm2·V–1 as measured under 241Am (5.48 MeV) alpha particles irradiation. Nevertheless, Pb2P2Se6 detectors with a thickness of 2 mm show reliable linear response under a series of radiation sources, including 241Am and 57Co γ-ray sources. A high X-ray sensitivity comparable to that of amorphous Se for Pb-rich Pb2P2Se6 detectors was realized, with the value of 68.3 μC·Gyair–1 cm–2 under 40 kVp Ag X-rays at an electrical field of 50 V·cm–1.