Engineering Radiative Energy Transfer and Directional Excitonic Emission in van der Waals Heterostructures

Abstract

Controlling excitonic energy transfer in 2D van der Waals (vdW) heterostructures is crucial for photonic and optoelectronic applications. Recent studies suggest that the interlayer energy transfer in vdW heterostructures is strongly correlated with the vertical interlayer spacing. However, the interlayer coupling with large separations (>20 nm) when the radiative energy transfer is dominant has not been studied yet. In this case, excitons as radiative dipole sources are able to control the light field. Here, the thickness dependency of radiative energy transfer in vertical vdW heterostructures of WS2 (tungsten disulfide)/hBN (hexagonal boron nitride)/WS2 is studied. The excitonic emission of WS2/hBN and WS2/hBN/WS2 heterostructures is engineered with the intensity ratios of heterostructures to monolayers ranging from 5% to 250%. More importantly, by changing the stacking order to control whether forward or backward emission is collected, a controllable directivity of the excitonic emission from 0.6 to 6.0 is achieved. In theory, the tunability to high‐index/mid‐index interferences and dipole–dipole far‐field coupling is attributed. The outcomes of the study on the radiative energy transfer of vdW heterostructures containing 1Ls (monolayers) with excitonic effects and MLs (multilayers) with high refractive indices will pave the way toward the realization of all vdW nanophotonics.

Van der Waals Heterostructures With Built‐In Mie Resonances For Polarization‐Sensitive Photodetection

“…Previous studies have focused on their optical effects and the intrinsic Mie-exciton coupling. [36][37][38][39][40][41] How to take advantages of strong optical resonances of nanopatterned TMDs to build photodetectors remains unresolved.…”

Nonlinear Nano‐Imaging of Interlayer Coupling in 2D Graphene‐Semiconductor Heterostructures

“…The range of timescales is in part attributed to variations in interlayer distance dependent on sample condition, [ 12,32,47–49 ] and raises the question about the role of spatial heterogeneities. Already, the distinction between interlayer charge and energy transfer in the competition with different intra‐ and interlayer radiative and non‐radiative processes is difficult in general.…”

“…[43] Similarly, theoretical studies [44] and time-resolved Raman and photoluminescence spectroscopy [45,46] have addressed the energy transfer dynamics, finding timescales of few-ps in MoSe 2 /graphene [44] and ≈4 ps in WS 2 /graphene. [45] The range of timescales is in part attributed to variations in interlayer distance dependent on sample condition, [12,32,[47][48][49] and raises the question about the role of spatial heterogeneities. Already, the distinction between interlayer charge and energy transfer in the competition with different intra-and interlayer radiative and non-radiative processes is difficult in general.…”