van der Waals (vdW) heterostructures provide a powerful method to control the alignment of energy bands of atomically thin 2D materials. Under light illumination, the optical responses are dominated by Coulomb-bound electron-hole quasiparticles, for example, excitons, trions, and biexcitons, whose contributions accordingly depend on the types of heterostructures. For type-II heterostructures, it has been well established that light excitation results in electrons and holes that are separated in different layers, and the radiative recombination is dominated by the interlayer excitons. On the contrary, little is known about the corresponding optical responses of type-I cases. Understanding the optical characteristics of type-I heterostructures is important to the full exploration of the quasiparticle physics of the 2D heterostacks. In this study, we performed optical spectroscopy on type-I vdW heterostacks composed of monolayer MoTe2 and WSe2. Photoluminescence and reflection contrast spectroscopy show that the light absorption and emission are dominated by the Coulomb-bound trions. Importantly, we observed that the MoTe2 trion emission gets stronger compared with the exciton emission under resonant light excitation to the WSe2 trion absorption state, especially in the WSe2/MoTe2/WSe2 heterotrilayer. A detailed study of photoluminescence excitation further reveals that the charge-transfer mechanism is likely responsible for our observation, which differs from the exciton-dominated dipole-dipole energy transfer in type-II structures. Our demonstration implies that the type-I vdW heterostack provides new opportunities to engineer the light-matter interactions through many-body Coulomb-bound states.
Bibliographical noteFunding Information:
This work was supported by the New Faculty Startup Fund from Seoul National University. H.B., S.L., M.N., and H.C. were supported by the NRF through the government of Korea (MSIP) (grants NRF-2018R1A2A1A05079060, NRF-2021R1A2C3005905), the Creative Materials Discovery Program (grant 2017M3D1A1040828), the Scalable Quantum Computer Technology Platform Center (grant 2019R1A5A1027055), and the Institute for Basic Science (IBS), Korea under project code IBS-R014-G1-2018-A1. H.C. was supported by LG Yonam Foundation of Korea. O.K. acknowledges the support of the Viterbi Fellowship of the Erna and Andrew Viterbi Department of Electrical Engineering, Technion, Israel, and of the Koret Foundation, CA, USA. E.B. is supported by the National Sciences and Engineering Research Council (NSERC) of Canada PostGraduate Scholarship for Doctoral program (PGS-D), PGSD3-502559-2017, and the National Science Foundation (NSF) newLAW program, award 1741691.
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All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Atomic and Molecular Physics, and Optics
- Electrical and Electronic Engineering