Layer-engineered interlayer charge transfer in WSe₂/WS₂ heterostructures

Abstract

The layer thickness determines the electronic structure of the two-dimensional material, leading to different band alignment, which are crucial for the transition metal dichalcogenides heterostructures. Here we investigated the heterostructure of WSe2/WS2 with different layer thicknesses by steady-state and transient absorption spectroscopy. We observed different ultrafast charge transfer behaviors in 1L-WSe2/2L-WS2 and 2L-WSe2/2L-WS2 fewlayer heterostructures. We demonstrate that the layer thickness determines the sequence of intralayer exciton relaxation and interlayer charge transfer. The valley transfer of the band edge induced by the layer thickness can effectively mediate the hot carrier transfer time and interlayer exciton lifetime. These provide us a deeper understanding of carrier dynamics in two-dimensional indirect bandgap semiconductor heterostructures.

Modulation and Optoelectronic Applications of van der Waals Interlayer Excitons

“…In addition, the assistance of optical structures, such as waveguides, surface plasmons, resonators, and so on, can further enhance the light-matter interaction, thereby optimizing the performance of optoelectronic devices . Moreover, influence factors, such as intrinsic properties of materials (thickness of layers, polarization, ferroelectricity, ...), manufacturing technics, etc., also should be considered to fabricate interface-clean, type-II aligned, momentum-matching heterostructures. From a single device to arrays. Due to the controllable synthesis of two-dimensional materials (thickness, morphology, size, orientation, etc.)…”

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

“…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.…”

Fast atomic crack kinking and branching in WS2

“…Transition metal dichalcogenides (TMDs) are two dimensional (2D) semiconductors with an MX 2 arrangement [1,2], where M represents a transition metal (e.g., Mo, W, Re) and X denotes a chalcogen (such as S, Se, Te). Each monolayer consists of transition metal atoms sandwiched between two layers of chalcogen atoms, resulting in a thickness of 6-7 Å. TMDs have garnered extensive attention in various fields such as optoelectronics, energy storage, and biomedicine [3,4], due to their exceptional properties, including the quantum confinement effect, direct band gaps, and remarkable transparency and flexibility [5].…”