Optical anisotropy of black phosphorus characterized by FTIR spectroscopy methods

The present study employs the FTIR spectroscopy methods, such as polarized transmittance measurements and the reflectance anisotropy spectroscopy technique, to characterize the optical properties of black phosphorus - a layered semiconductor with a narrow band gap. Our results reveal a notable crystal absorption anisotropy within the 0.26-0.42 eV range with strong linear dichroism, wherein a polarization-dependent feature is observed in the reflectance anisotropy spectra with a maximum near 0.33 eV. This feature is believed to be related to a direct interband transition E₀, which is permitted for linearly polarized incident radiation along the AC crystal direction and forbidden for the ZZ direction.