Identifying the Intermediate Free-Carrier Dynamics Across the Charge Separation in Monolayer MoS₂/ReSe₂ Heterostructures

Abstract

Van der Waals heterostructures composed of different two-dimensional films offer a unique platform for engineering and promoting photoelectric performances, which highly demands the understanding of photocarrier dynamics. Herein, large-scale vertically stacked heterostructures with MoS2 and ReSe2 monolayers are fabricated. Correspondingly, the carrier dynamics have been thoroughly investigated using different ultrafast spectroscopies, including Terahertz (THz) emission spectroscopy, time-resolved THz spectroscopy (TRTS), and near-infrared optical pump–probe spectroscopy (OPPS), providing complementary dynamic information for the out-of-plane charge separation and in-plane charge transport at different stages. The initial charge transfer (CT) within the first 170 fs, generating a transient directional current, is directly demonstrated by the THz emissions. Furthermore, the TRTS explicitly unveils an intermediate free-carrier relaxation pathway, featuring a pronounced augmentation of THz photoconductivity compared to the isolated ReSe2 layer, which likely contains the evolution from immigrant hot charged free carriers to bounded interlayer excitons (∼0.7 ps) and the surface defect trapping (∼13 ps). In addition, the OPPS reveals a distinct enhancement in the saturable absorption along with long-lived dynamics (∼365 ps), which originated from the CT and interlayer exciton recombination. Our work provides comprehensive insight into the photocarrier dynamics across the charge separation and will help with the development of optoelectronic devices based on ReSe2–MoS2 heterostructures.

Phosphorus-Doped Single-Crystalline Quaternary Sulfide Nanobelts Enable Efficient Visible-Light Photocatalytic Hydrogen Evolution

“…Correspondingly, the transient complex conductivities in the frequency domain are extracted and displayed in Figure S26. The THz conductivities can be reproduced by the Drude–Smith models, emphasizing the free-carrier transport with preferential backscattering characterization for both CZIS and CZIS-P nanobelts. − The real parts of transient THz conductivity, Re (Δσ), as the function of pump-probe time delays for CZIS and CZIS-P nanobelts are plotted in Figure e (Figure S27), which match well with the biexponential functions. The obtained slow time constants are about 38 and 45 ps for CZIS and CZIS-P samples, respectively, while the fast time constant is 2.5 ps for each sample.…”

Structure modulation of two-dimensional transition metal chalcogenides: recent advances in methodology, mechanism and applications

“…317,318 The interlayer excitons with long lifetimes are not only observed in the six conventional heterostructures but also reported in the new type-II ones, such as MoS 2 /ReSe 2 heterostructures. 319 Besides, incoherent interlayer excitons are generated from electrons in one layer and holes tunnelled from the same layer to the other, with the assistance of the emission and adsorption of phonons. 320 Interlayer excitons with reduced binding energies benefit from the enhanced heterointerface screening with longer formation times compared with intralayer ones.…”

2D Rhenium Dichalcogenides: From Fundamental Properties to Recent Advances in Photodetector Technology

“…[ 232 ] Similar free carrier contribution was observed in ReSe 2 /MoS 2 heterostructure made of vertically stacked monolayers due to the occurrence of intermediate relaxation channels. [ 233 ] Furthermore, heterostructures permit long‐lived relaxation pathway associated with interlayer excitons and prolong the photocarrier life time. While the direction and speed of exciton diffusion can be controlled through strain and dielectric engineering, with studies reporting nearly ballistic exciton diffusion in MoSe 2 at low temperature under uniaxial strain, [ 234 ] the experimental observation of larger diffusion coefficient for excitons along the Re chain direction [ 108 ] makes the ReX 2 a potential candidate for polarization sensitive photodetectors.…”

“…Time‐resolved THz and optical pump‐probe spectroscopic studies provide a strong evidence for pronounced THz photoconductivity and long‐lived relaxation pathway associated with interlayer excitons. [ 233 ] For a heterostructure of few layer ReSe 2 and monolayer MoS 2 , the photodetector figures of merit were R = 3.52 AW −1 , D = 10 11 Jones, and rise/decay times of 5/9.1 µs at 638 nm. [ 343 ] The strong photovoltaic effect in WSe 2 /ReSe 2 heterostructure can be utilized to construct a self‐powered photodetector.…”