Preparation and characterization of free-standing BiI3 single-crystal flakes for X-ray detection application

Free-standing BiI 3 single-crystal flakes with a rhombohedral appearance and 10–100 µm in thickness were prepared by using physical vapor transport method. The (00 l ) ( l  = 3, 6, 9, 12) planes of the as-grown crystal present a distribution of layered structure and approximatively atomically smooth surface with 1.3–1.7 nm step height and roughness average 0.38–0.65 nm. Both planar and coplanar electrode configuration devices for X-ray detection were fabricated with the as-grown BiI 3 single crystals and the dark resistivity 5.8–6.4 × 10 11  Ω cm and 1.2–1.8 × 10 11  Ω cm at room temperature were obtained, respectively. A low dark current or high resistivity for planar device is on account of carrier scattering from the I–Bi–I interlayer van der Waals bonding interface. A high net photocurrent and good sensitivity 1.22–1.36 × 10 4  µC/Gy air /cm 2 under X-ray excitation were also obtained with planar device owing to the uniform electric field distribution and high charge collection efficiency.