Energy-valley-dependent charge transfer in few-layer transition metal dichalcogenide heterostructures

The effect of the energy valley on interlayer charge transfer in transition metal dichalcogenide (TMD) heterostructures is studied by transient absorption spectroscopy and density functional theory. First-principles calculations confirm that the Λmin valley in the conduction band of few-layer WSe2 evolves from above its K valley in the monolayer (1L) to below it in 4L. Heterostructure samples of nL-WSe2/1L-MoS2, where n=1,2,3, and 4, are obtained by mechanical exfoliation and dry transfer. Photoluminescence spectroscopy reveals a thickness-dependent WSe2 band structure and efficient interlayer charge transfer. Transient absorption measurements show that the electron transfer time from the Λmin valley of 4L WSe2 to the K valley of MoS2 is on the order of 30 ps. This process is much slower than the K-K charge transfer in 1L/1L TMD heterostructures. The momentum-indirect interlayer excitons formed after charge transfer have lifetimes >1 ns. © 2023 American Physical Society.