Observation of enhanced WSe2 exciton–exciton annihilation in WSe2/Gr/hBN heterostructure

Abstract

Due to strong quantum confinement effects and novel physical properties, two-dimensional transition metal dichalcogenides (TMDCs) as well as their heterostructures provide an attractive platform for studying excitonic effects and many-body interactions. However, manipulation on the excitonic effect in TMDCs remains challenge owing to the complex interplay of various factors. In this Letter, we report large exciton peak redshift and enhanced exciton–exciton annihilation in WSe2/Gr/hBN heterostructures investigated with static and transient optical spectroscopy. The pronounced redshift of exciton energy in the triple layer heterostructure arises from the charge transfer effect between graphene and WSe2, which leads to the reduction of the WSe2 exciton binding energy significantly due to the Coulomb screening effect. As a result, the reduced exciton binding energy increases the exciton delocalization in the WSe2 layer, leading to an increased probability of exciton–exciton collisions, which results in fast exciton annihilation rate. This study demonstrates the impact of graphene layer on exciton energy as well as the relaxation dynamics in WSe2/Gr/hBN heterostructures, which provides insights into the understanding of quasiparticle physics and many-body interactions in 2D materials.