Infrared interlayer excitons in MoS2/WSe2 van der Waals heterostructures

Ultrafast Charge-Transfer Dynamics in Twisted MoS2/WSe2 Heterostructures

“…(g) Schematic band alignment of MoS 2 /WSe 2 showing the individual K-points of both materials and the hybridized Γ-point . The dashed ellipses mark the previously reported K–K and Γ–K interlayer excitons. , (h) Corresponding hexagonal Brillouin zones of the studied heterostructures for the three stacking angles 9° (red), 16° (green), and 52° (blue). The colored solid lines represent the respective MoS 2 Brillouin zones rotated relative to the WSe 2 (dotted maroon line).…”

“…The misaligned sample shows the longest lifetime (467 ± 16 ps), the quasi-3R stacked sample shows an intermediate lifetime (309 ± 12 ps), and the quasi-2H stacked sample shows the shortest lifetime (158 ± 10 ps). The enhanced lifetime for the misaligned sample could be an indication for the absence of the radiative decay channel as it was reported recently . The difference in lifetime between quasi-2H and quasi-3R can then be explained by the same reasoning as the enhanced transfer.…”

“…The intralayer A-exciton and trion energies of MoS 2 and WSe 2 , in contrast, have not shown a distinct dependence on the interlayer twist but only a minor 25 meV shift in energy due to the modified dielectric environment in the heterobilayers . Recently, also momentum-space direct K–K photoluminescence at ≈1.0 eV has been observed for well-aligned MoS 2 /WSe 2 heterostructures . In the present study, we want to elucidate the corresponding ultrafast dynamics in dependence of the stacking angle for three selected stacking angles: 9° (referred to as quasi-3R), 52° (quasi-2H), and 16° (misaligned).…”

Dispersion Property and Evolution of Second Harmonic Generation Pattern in Type-I and Type-II van der Waals Heterostructures

“…The band alignments of MoTe 2 /WSe 2 and MoSe 2 /WSe 2 vdWHs suggest that they belong to type I and type II, respectively, as shown in Figure S1b. The band structures of MoTe 2 /WSe 2 and MoSe 2 /WSe 2 vdWHs reveal that effective photoluminescence enhancement from narrow band gap materials (i.e., MoTe 2 in MoTe 2 /WSe 2 ) can be achieved in type-I vdWHs , and ultrafast charge separation can be achieved through the interface in type-II vdWHs. − After photoexcitation, carriers can be generated by the transition between different valleys from the band structures of vdWHs. As shown in Figure a, the momentum-indirect interlayer transition (M–K; Q–K; Γ–Q) and intralayer transition (M–Q; K–Q; Γ–Q) from different band valleys can occur, whereas the momentum-direct interlayer transition (K–K) and intralayer transition (Q–Q) can take place by the electron and hole from the band valleys at the same K points in the highest VB and lowest CB in MoTe 2 /WSe 2 vdWHs.…”

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

“…The understanding of carrier dynamics is essential for laying a foundation for the development of optoelectronic devices. ,, Compared with individual 2D-TMDs, out-of-plane charge separation adds the degree of freedom of photocarrier dynamics in vertically stacked TMDs heterostructures. − ,, Because of the difference of band alignment between different components, the electrons in the conduction band or the holes in the valence band will transfer to another conduction (valence) band with lower energy, and therefore the interlayer excitons can be formed. − Since the ultrafast time scale (∼50 fs) of charge transfer (CT) in MoS 2 /WS 2 heterostructures has been experimentally revealed, the CT and interlayer exciton dynamics in vdW heterostructures, such as MoS 2 /WS 2 and MoS 2 /MoSe 2 systems, have been extensively investigated with time-resolved optical spectroscopy. ,,,,, The obtained consensus is that the CT generally takes place with high efficiency and a high rate within a subpicosecond time scale, ,,,− although it stands as a puzzle considering the large mismatch of parallel momentum of electron immigrating between the adjacent layers. , Accordingly, different CT mechanisms, including the collective motion of excitons, donor–acceptor delocalization, phonon excitation and assistance, − energy band couplings, interlayer hopping, and adiabatic transfer, have been proposed theoretically. The identifications for different excitation species or intermediate states, such as intralayer excitons, interlayer excitons, free electron–hole plasmas, and delocalized states, as well as the corresponding formation and relaxation, are prerequisites for the establishment of a complete photocarrier dynamics scenario.…”