Cu₂I₂Se₆: A Metal-Inorganic Framework Wide-Bandgap Semiconductor for Photon Detection at Room Temperature

Cu₂I₂Se₆ is a new wide-bandgap semiconductor with high stability and great potential toward hard radiation and photon detection. Cu₂I₂Se₆ crystallizes in the rhombohedral R3̅m space group with a density of d = 5.287 g·cm^-3 and a wide bandgap E_g of 1.95 eV. First-principles electronic band structure calculations at the density functional theory level indicate an indirect bandgap and a low electron effective mass m_e* of 0.32. The congruently melting compound was grown in centimeter-size Cu₂I₂Se₆ single crystals using a vertical Bridgman method. A high electric resistivity of ∼10¹² Ω·cm is readily achieved, and detectors made of Cu₂I₂Se₆ single crystals demonstrate high photosensitivity to Ag Kα X-rays (22.4 keV) and show spectroscopic performance with energy resolutions under ²⁴¹Am α-particles (5.5 MeV) radiation. The electron mobility is measured by a time-of-flight technique to be ∼46 cm²·V^-1·s^-1. This value is comparable to that of one of the leading γ-ray detector materials, TlBr, and is a factor of 30 higher than mobility values obtained for amorphous Se for X-ray detection.