Hot Carrier Transfer in a Graphene/PtSe₂ Heterostructure Tuned by a Substrate-Introduced Effective Electric Field

Abstract

The van der Waals heterojunction involving graphene (Gr) with transition metal dichalcogenides (TMDs) is regarded as a promising structure for its outstanding performance in optoelectronic response. The electron–hole thermalization has been deemed to be the main reason for the subband gap excitation charge transfer from Gr to TMDs. However, the role of the intricate interlayer interaction of Gr and TMDs still requires intensive investigation. Here, we have investigated the photocarrier dynamics in a five-layer PtSe2/Gr heterojunction by using time-resolved optical pump and terahertz probe spectroscopy. Interestingly, after photoexcitation, electron transfer from PtSe2 to Gr has been demonstrated successfully in the PtSe2/Gr/substrate heterojunction; by contrast, no observable charge transfer occurs in the Gr/PtSe2/substrate heterostructure. The prominent difference for the different stacking sequences between Gr and PtSe2 can be ascribed to the effective electric field introduced by the fused silica substrate. A physical picture accounting for the effective electric field introduced by the substrate has been proposed to interpret the charge transfer process in the TMD/Gr heterostructure. More importantly, the electric field induced by the substrate plays a dominant role in controlling the charge transfer pathway in the TMDs/Gr heterojunction. This study not only sheds light on the substrate engineering of the van der Waals heterojunction but also provides new insight into the layer interaction dynamics in the Gr/TMD heterojunction.

Role of the Optical–Acoustic Phonon Interaction in the Ultrafast Cooling Process of CVD Graphene

“…As the sample films are thin, Δ T / T 0 is related to the photoinduced sheet photoconductivity by , where n = 1.95 is the refractive index of the fused silica substrate, and Z 0 = 377 is the free space impedance. The temporal dynamics of the terahertz conductivity were fitted using −Δσ­(Δ t ) = A ·e – t /τ decay + C , where τ decay is the cooling time constant of the supercollision process and C represents the longitudinal thermal diffusion process, which is considered as a plateau under the employed conditions. , …”

Tunable ultrafast electron transfer in WSe2–graphene heterostructures enabled by atomic stacking order

“…In addition to the controversy regarding the CT mechanism, the substrate effect has also been reported to significantly affect the CT process. [17][18][19] Notably, substrates affect 2D materials via either charge transfer or dielectric screening. 19 As the charge screening length is greater than the atomic layer thickness, dielectric screening via substrates can influence both layers in heterostructures.…”

Ultrafast Dynamics of Defect-Assisted Auger Process in PdSe2 Films: Synergistic Interaction between Defect Trapping and Auger Effect

“…The possible mechanisms that can be responsible for prolonging or shortening the characteristic time of pump-induced carrier dynamics include phonon-assisted relaxation, − exciton–exciton annihilation (EEA), , Auger process, , and defect-assisted relaxation. − We first rule out the phonon-assisted process, which depends strongly on the lattice temperature, because the energy dissipation during the relaxation process needs to satisfy momentum conservation . Our temperature independence of dynamics shown in Figure suggests the phonon-assisted process is not important for both fast and slow relaxation processes.…”