Infrared optical constants <i>n</i> , <i>κ</i> , and absorption of topological insulator BiSb thin films determined by the reflectance-transmittance technique

In this work, we measure the infrared optical constants ( n , κ ) of topological insulator BiSb thin films using the reflectance-transmittance method. Using the obtained ( n , κ ), we reveal that Bi, Bi 0.9 Sb 0.1 , and Bi 0.85 Sb 0.15 show absorption of about 30% for film thicknesses around 20 nm and a large refractive index ranging from 6 to 9 in the infrared region. Our results suggest that BiSb has strong potential as a material for MIR detectors.