Interlayer Coupling and Gate-Tunable Excitons in Transition Metal Dichalcogenide Heterostructures

Abstract

Bilayer van der Waals (vdW) heterostructures such as MoS2/WS2 and MoSe2/WSe2 have attracted much attention recently, particularly because of their type II band alignments and the formation of interlayer exciton as the lowest-energy excitonic state. In this work, we calculate the electronic and optical properties of such heterostructures with the first-principles GW+Bethe-Salpeter Equation (BSE) method and reveal the important role of interlayer coupling in deciding the excited-state properties, including the band alignment and excitonic properties. Our calculation shows that due to the interlayer coupling, the low energy excitons can be widely tunable by a vertical gate field. In particular, the dipole oscillator strength and radiative lifetime of the lowest energy exciton in these bilayer heterostructures is varied by over an order of magnitude within a practical external gate field. We also build a simple model that captures the essential physics behind this tunability and allows the extension of the ab initio results to a large range of electric fields. Our work clarifies the physical picture of interlayer excitons in bilayer vdW heterostructures and predicts a wide range of gate-tunable excited-state properties of 2D optoelectronic devices.

Control of the orbital character of indirect excitons in MoS2/WS2 heterobilayers

“…Due to hybridization, moiré effects and altered dielectric environment [2-6, 19, 20], real TMDC HBs can have a much more complicated band structure with fascinating and so far only little explored electronic and optical properties based on the orbital character of the involved electronic states. For the HBs embedded in a field-effect device, an anti-crossing behaviour of IXs is expected based on the residual coupling of electronic states in the two TMDC layers [19] accompanied by a gradual change of the exciton nature from primarily interlayer to primarily intralyer [cf. Figure 1a].…”

Light–matter interaction in van der Waals hetero-structures

“…As demonstrated in figure 5d, even triplet IX emission has been reported for hBN encapsulated MoS 2 /WS 2 heterobilayers and interpreted as momentum direct and indirect IX transitions involving electron states at K and the hybridized Σ valley and hole states at K and the hybridized Γ valley indicated in figure 5e [55,95,128,133,135]. Finite coupling of electronic states and valley selective hybridization together with the finite dipole moment of IX allows to tune and engineer the properties of the bound exciton states by application of an electric field normal to the hetero-bilayers utilized by gate electrodes [55,133,152]. Electric field control of layer index, orbital character, lifetime and emission energy of indirect excitons in MoS 2 /WS 2 hetero-bilayers embedded in an vdW field effected structure allows for the design of novel vdW based quantum-nano architectures as e.g.…”

Multiphonon Raman Scattering in Transition Metal Dichalcogenide Double Layers

“…This property holds the potential applications for creating excitonic signal processing devices and excitonic circuits with sufficient lifetime. In addition, the electron–hole separation results in a permanent electric dipole moment, which is convenient to modulate by the external electric field . These fascinating properties of interlayer excitons also allow for exploring nonlinear optical phenomena in these 2D systems.…”

“…In addition, the electron-hole separation results in a permanent electric dipole moment, which is convenient to modulate by the external electric field. [20,21] These fascinating properties of interlayer excitons also allow for exploring nonlinear optical phenomena in these 2D systems.…”

“…One can see that Huang-Rhys factor varies significantly with the increase in polarization constant. Several recent experiments [20,[40][41][42] proved that carrier-phonon coupling is affected sensitively by the surrounding dielectric environment, which can be reflected by this polarization constant. However, the detailed studies for the relationship between the dielectric environment and this polarization constant are beyond this article.…”