Refined Synthesis and Crystal Growth of Pb₂P₂Se₆ for Hard Radiation Detectors

The refined synthesis and optimized crystal growth of high quality Pb₂P₂Se₆ single crystals are reported. Improved experimental procedures were implemented to reduce the oxygen contamination and improve the stoichiometry of the single crystal samples. The impact of oxygen contamination and the nature of the stoichiometry deviation in the Pb₂P₂Se₆ system were studied by first-principles density functional theory (DFT) electronic structure calculations as well as experimental methods. The DFT calculations indicated that the presence of interstitial oxygen atoms (O_int) leads to the formation of a deep level located near the middle of the gap, as well as a shallow acceptor level near the valence band maximum. In addition, total energy calculations of the heat of formation of Pb₂P₂Se₆ suggest that the region of thermodynamic stability is sufficiently wide. By refining the preparative procedures, high quality Pb₂P₂Se₆ single crystal samples were reproducibly obtained. These Pb₂P₂Se₆ single crystals exhibited excellent optical transparency, electrical resistivity in the range of 10¹¹ Ω·cm, and a significant increase in photoconductivity. Infrared photoluminescence of the Pb₂P₂Se₆ single crystals was observed over the temperature range of 15-75 K. Detectors fabricated from boules yielded a clear spectroscopic response to both Ag Kα X-ray and ⁵⁷Co γ-ray radiation. The electron and hole mobility-lifetime product (μτ) of the current Pb₂P₂Se₆ detectors were estimated to be 3.1 × 10^-4 and 4.8 × 10^-5 cm²/V, respectively.