Anisotropic Electron-Photon and Electron-Phonon Interactions in Black Phosphorus

Abstract

Orthorhombic black phosphorus (BP) and other layered materials, such as gallium telluride (GaTe) and tin selenide (SnSe), stand out among two-dimensional (2D) materials owing to their anisotropic in-plane structure. This anisotropy adds a new dimension to the properties of 2D materials and stimulates the development of angle-resolved photonics and electronics. However, understanding the effect of anisotropy has remained unsatisfactory to date, as shown by a number of inconsistencies in the recent literature. We use angle-resolved absorption and Raman spectroscopies to investigate the role of anisotropy on the electron-photon and electron-phonon interactions in BP. We highlight, both experimentally and theoretically, a nontrivial dependence between anisotropy and flake thickness and photon and phonon energies. We show that once understood, the anisotropic optical absorption appears to be a reliable and simple way to identify the crystalline orientation of BP, which cannot be determined from Raman spectroscopy without the explicit consideration of excitation wavelength and flake thickness, as commonly used previously.

Narrow-band anisotropic electronic structure of ReS2

“…Angle-dependent Raman scattering measurements of these samples show strong anisotropy in the 214 cm −1 peak intensity with clear twofold symmetry, as seen in recent reports [9,17,18].…”

Booming Development of Group IV–VI Semiconductors: Fresh Blood of 2D Family

“…Furthermore, polarized Raman characterization was implemented to explore the polarization dependence due to the reduced symmetry of the orthorhombic phase. The authors inspected that the orthorhombic phase SnS nanosheets exhibit strong anisotropic Raman response similar with black phosphorous150 and ReS 2 151, 152, 153, 154. The parallel‐polarization configuration strongly suggests that the A 1g mode (190.7 cm −1 ) can be employed to detect crystallographic orientation of the SnS flakes because of the A 1g mode reaches the maximum as illumination light polarization is parallel to armchair direction of the SnS flakes, which may also exist in other group IV orthorhombic phases such as SnSe, GeS, and GeSe.…”

Evolution of electronic structure of few-layer phosphorene from angle-resolved photoemission spectroscopy of black phosphorous

“…In addition, it was recently demonstrated that the exciton binding energy depends on the type of substrate due to environmental effects on the dielectric constant [22]. Phosphorene also shows a strong optical anisotropy for light polarization in the two high symmetry directions which is related to the large anisotropy of the electron effective masses [21,23,24,28,29].…”