Photocarrier dynamics in monolayer phosphorene and bulk black phosphorus

Abstract

We report a combined theoretical and experimental study on photocarrier dynamics in monolayer phosphorene and bulk black phosphorus. Samples of monolayer phosphorene and bulk black phosphorus were fabricated by mechanical exfoliation, identified according to their reflective contrasts, and protected by covering them with hexagonal boron nitride layers. Photocarrier dynamics in these samples was studied by an ultrafast pump-probe technique. The photocarrier lifetime of monolayer phosphorene was found to be about 700 ps, which is about 9 times longer than that of bulk black phosphorus. This trend was reproduced in our calculations based on ab initio nonadiabatic molecular dynamics combined with time-domain density functional theory in the Kohn-Sham representation, and can be attributed to the smaller bandgap and stronger nonadiabatic coupling in bulk. The transient absorption response was also found to be dependent on the sample orientation with respect to the pump polarization, which is consistent with the previously reported anisotropic absorption of phosphorene. In addition, an oscillating component of the differential reflection signal at early probe delays was observed in the bulk sample and was attributed to the layer-breathing phonon mode with an energy of about 1 meV and a decay time of about 1.35 ps. These results provide valuable information for application of monolayer phosphorene in optoelectronics.

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

“…However, the optical conductivity of hot carriers, i.e., excited quasiequilibrium states by the pump light, is highly anisotropic, which may lead to novel device design such as high‐speed polarization devices based on BP. The photocarrier lifetime of monolayer BP is characterized to be about 700 ps that is nearly nine times longer than that of the bulk counterpart . The diffusion coefficient D along the zigzag direction is about 16 times smaller than that along the armchair direction.…”

“…The photocarrier lifetime of monolayer BP is characterized to be about 700 ps that is nearly nine times longer than that of the bulk counterpart. [106] The diffusion coefficient D along the zigzag direction is about 16 times smaller than that along the armchair direction. In associated with the isotropic carrier lifetime τ, the carrier diffusion length (L = (Dτ) 1/2 ) is four times larger along the armchair direction than that along the zigzag direction.…”

“…Theoretically, this polarization‐dependent absorption is robust over a wide energy range spanning from 0.33 eV (MIR) up to 3.0 eV (UV) . The significant anisotropic optical absorption of BP leads to strong anisotropy manifested in other related optical properties such as the optical contrast, Raman spectroscopy, PL spectroscopy, photocurrent spectroscopy, and photocarrier dynamics …”

“…[93] The significant anisotropic optical absorption of BP leads to strong anisotropy manifested in other related optical properties such as the optical contrast, [95] Raman spectroscopy, [96][97][98][99][100][101] PL spectroscopy, [86,102] photocurrent spectroscopy, [93,103] and photocarrier dynamics. [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.…”

Interlayer charge transfer in ReS2/WS2 van der Waals heterostructures

“…First, a ReS 2 flake containing 1L and 2L regions was mechanically exfoliated on a polydimethylsiloxane (PDMS) substrate. Since the substrate (about 1 mm) is much thicker than the ReS 2 flake and is transparent, the optical contrast of the flake is proportional to its thickness 11,[51][52][53][54] . By investigating a large number of thin flakes, we establish that the contrast of 1L is about 15.5%.…”