Defect engineering of BiI₃ single crystals: Enhanced electrical and radiation performance for room temperature gamma-ray detection

Undoped and Sb-doped BiI₃ (SBI) single crystals are grown via the vertical Bridgman growth technique. Electrical properties, such as resistivity and leakage current, in addition to radiation response measurements are performed on both BiI₃ and SBI single crystal detectors. The resistivity of SBI (2.6310⁹ Ω·cm) increases by an order of magnitude compared to that of BiI₃ (1.45 × 10⁸ Ω·cm). Furthermore, leakage currents of SBI (10^-2 μA/cm²) decrease by four orders magnitude relative to BiI ₃. The radiation response of the SBI indicates that less polarization exists under bias for prolonged periods of time, making SBI a promising material for use in gamma-ray detector applications. Density functional theory (DFT) calculations predict that Sb forms strong covalent bonds with neighboring iodine ions and that the Sb-I dimer can be formed when Sb is doped into the BiI₃ lattice. In addition, defect modeling verifies that substitution of Bi ions with Sb and incorporation of Sb in iodine vacancy sites can effectively decrease the formation and migration of iodine vacancies, which significantly improves radiation detection performance of the material.