Visualizing Optical Phase Anisotropy in Black Phosphorus

Abstract

Layered black phosphorus has triggered enormous interest since its recent emergence. Compared to most other two-dimensional materials, black phosphorus features a moderate band gap and pronounced in-plane anisotropy, which stems from the unique atomicpuckering crystal structure. The future potential of black phosphorus in optoelectronics demands a deeper understanding of its unique anisotropic behavior. In particular, the phase information of light when interacting with the material is imperative for many applications in the optical regime.In this work we have comprehensively studied a wide range of optical anisotropic properties of black phosphorus, including the Raman scattering, extinction spectra, and phase retardance by utilizing conventional spectral measurements and a uniquely developed interferometric spectroscopy and imaging technique. The phase retardance of light passed through black phosphorus is exploited in conjunction with polarization interferometric techniques to demonstrate an optical contrast an order of magnitude higher than a purely polarization-based measurement could offer.The past decade has witnessed the explosive development of two-dimensional (2D) materials, whose ever-expanding family now represents one of the most exciting frontiers in physics and materials science. The intriguing physical properties of 2D materials, primarily derived from their out of plane quantum confinement and the strong in-plane bonding, have enabled diverse applications in electronics, mechanics, as well as optics and photonics. 1-7 Among this new class of material, graphene has laid the foundation for the 2D frontier of nanoscale optical applications in integrated nano-photonics, 8, 9 ultrafast light detection, 10, 11 and plasmonics. 12, 13 Now, this field is quickly being populated with other materials such as transition metal dichalcogenide (TMDC) which exhibit exotic properties of their own. For instance, TMDC has demonstrated optical helicity controlled valley polarization which opens pathways for valleytronics. 14-17 Recently, layered black phosphorus (BP) has been reintroduced to the family from its dormancy a century ago. [18][19][20][21] As a new member of the 2D material class, BP bridges the semi-metallic graphene and semiconducting TMDC with a moderate band gap. [22][23][24][25][26] Compared to most other 2D materials, whose electronic and photonic properties are isotropic in-plane, the most distinguishable property of BP is its in-plane anisotropy stemming from the unique atomic-puckering crystal structure. Previous studies have revealed a range of intriguing anisotropic behaviors of BP in terms of its optical spectrum, Raman scattering, light absorption, photo-detection, and electrical conductivity. 27-34 While these properties reported in the literature have formed a valuable basis, many applications in the optical domain demand more information regarding the wave characteristics of the interacting light with the BP medium, specifically its phase. Moreover, the manipulation of the phase retardan...

Optical and Optoelectronic Properties of Black Phosphorus and Recent Photonic and Optoelectronic Applications

“…The anisotropic PL spectra of mono‐ and few‐layer BP are closely related to the anisotropic absorption spectra and share the same symmetry origin . In monolayer BP, the polarization‐resolved PL spectra of monolayer BP show nearly perfect linear dichroism .…”

“…[104][105][106] The anisotropic PL spectra of mono-and few-layer BP are closely related to the anisotropic absorption spectra and share the same symmetry origin. [93,107,108] In monolayer BP, the polarization-resolved PL spectra of monolayer BP show nearly perfect linear dichroism. [86] The reduced dimension of ultrathin BP also features a prominent excitonic effect because of the suppressed screening effect and strong Coulomb interaction, [109] giving rise to a high exciton binding energy.…”

Mid-infrared Polarized Emission from Black Phosphorus Light-Emitting Diodes

“…The atomic crystal structure of BP consists of layered sp 3 -hybridized phosphorus atoms with distinct configurations along two orientations termed the armchair (AC) and zigzag (ZZ) directions. This gives rise to strong in-plane anisotropy for thermal conduction 18,19 , carrier transport and optical absorption 20,21,22,23,24 . In the context of optoelectronics, one of the most interesting properties of BP is its widely tunable bandgap and the fact that it is a direct bandgap material from the bulk down to bilayers.…”

Spectral Responsivity and Photoconductive Gain in Thin Film Black Phosphorus Photodetectors

“…The atomic crystal structure of black phosphorus consists of layered sp 3 -hybridized phosphorus atoms with distinct configurations along two directions, i.e. armchair (AC) and zigzag (ZZ), which lead to strong in-plane anisotropic physical properties, such as thermal conduction 16,17 , carrier transport and optical absorption [18][19][20][21][22] . In addition, the bandgap of BP is highly tunable by varying the number of layers.…”