Ultrafast charge transfer and carrier dynamics in a WS₂/MoSe₂ few-layer van der Waals heterostructure

Abstract

Photocarrier dynamics including interlayer charge transfer and intralayer valley scattering are studied in a heterostructure formed by trilayers of WS2 and MoSe2. The sample is fabricated by mechanical exfoliation and...

Layer-engineered interlayer charge transfer in WSe2/WS2 heterostructures

“…Thus the total 2L/2L hole relaxation process is also slower than that of 1L/2L, due to the more need of phonon assistance. Therefore, we suggest that, unlike previous studies for van der Waals bilayer heterostructures, the few-layer material increases the overall hot carrier relaxation time due to the band edges of Λ and Γ valley mediating the intervalley relaxation and interlayer CT [33]. It also leads to the transfer of intralayer excitons to interlayer excitons and the extension of exciton lifetime.…”

Ultrafast Laser Processing of 2D Materials: Novel Routes to Advanced Devices

“…Furthermore, the last decade studies have shown that 2DM are perfect candidates for multilayer heterostructures formation without the constraint of lattice matching. [188][189][190][191] This enables ultrafast electron transfer between heterolayers, [192][193][194][195] due to substantial changes in the electronic structure of the 2D monolayers in vdW structures. Additionally, the high electron mobility within the graphene conduction band provides rapid delocalization of the transferred electrons and significantly enhances charge transport with timescales as short as sub-fs.…”

Ultrafast Interlayer Charge Transfer Outcompeting Intralayer Valley Relaxation in Few-Layer 2D Heterostructures

“…A robust ultrafast (<100 fs) interlayer charge transfer has been generally observed in type II HSs, regardless of configurations, twisting angles, or dielectric environments. − Considering the momentum mismatch between donating and accepting K valleys in randomly orientated HSs, the origin for such robust ultrafast charge transfer behavior is unclear yet, and a widely invoked mechanism is electron transfer through a hybridized Q (denoted as T or Λ in some literatures) valley by phonon scattering (Figure ). ,,− …”

“…Previous charge transfer studies on TMD HSs have mostly focused on monolayer (1L) semiconductors with a direct bandgap where photoexcited electron/hole charges occupy and transfer from the K valley of one TMD layer to that of another layer. Only until very recently have HSs constituted of few-layer TMDs gained research attention. − The electronic structure of few-layer TMDs can be very different from that of a monolayer due to the interlayer coupling effect. − For example, the band structure of WSe 2 and WS 2 evolves from a direct bandgap in the monolayer to an indirect one in the bilayer or more, with the conduction band minimum (CBM) and valence band maximum (VBM) shifting from K to lower energy Q and Γ valleys, respectively. , While light excitation can only couple to the bright excitons at the K valley with negligible layer dependence, the presence of lower-lying dark valleys in few-layer TMDs should play a preeminent role in determining the photoexcitation charge transfer dynamics, which is yet to be fully unraveled. The study of few-layer TMD HSs with a lower lying Q valley can shed light on the role of the Q valley on the ultrafast charge transfer dynamics in TMD HSs.…”