Optical absorption of interlayer excitons in transition-metal dichalcogenide heterostructures

Abstract

Interlayer excitons, electron-hole pairs bound across two monolayer van der Waals semiconductors, offer promising electrical tunability and localizability. Because such excitons display weak electron-hole overlap, most studies have examined only the lowest-energy excitons through photoluminescence. We directly measured the dielectric response of interlayer excitons, which we accessed using their static electric dipole moment. We thereby determined an intrinsic radiative lifetime of 0.40 nanoseconds for the lowest direct-gap interlayer exciton in a tungsten diselenide/molybdenum diselenide heterostructure. We found that differences in electric field and twist angle induced trends in exciton transition strengths and energies, which could be related to wave function overlap, moiré confinement, and atomic reconstruction. Through comparison with photoluminescence spectra, this study identifies a momentum-indirect emission mechanism. Characterization of the absorption is key for applications relying on light-matter interactions.

Electrically tunable two-dimensional heterojunctions for miniaturized near-infrared spectrometers

“…However, the spatial separation between electrons in CBM and holes in VBM leads to a very small overlap between their wavefunctions, resulting in the weak transition dipole moment < Ψ 1 | M | Ψ 2 >. Hence, the interlayer oscillator strength is approximately at least 2 orders of magnitude smaller than that of intralayer transition 24 , 25 , and it is thus difficult to subsequently measure the gate-voltage tunable spectral photocurrents. More overlaps between electron wavefunction and hole wavefunction could enhance the transition dipole moment as well, which may be achieved by reducing the interlayer distance 34 , 35 by using hydrostatic pressure in a diamond anvil cell 36 , which is not easy to maintain for practical applications.…”

“…The van der Waals heterojunctions (vdWH) formed between distinct 2D transition metal dichalcogenides (TMDs) with type II energy band structure alignment provides a versatile platform for exploring interlayer excitons [20][21][22][23] . With the conduction band minimum (CBM) and valence band maximum (VBM) of the heterojunction localize in different layers, such typical type II heterojunctions opens a tunable degree of freedom to engineering interlayer optical transition in the IR regime beyond the limit of the intrinsic optical band gap of the constituent material 24 . Indeed, direct observation of interlayer optical excitation (IEX) infrared photoresponse was reported 25 .…”

Versatile van der Waals heterostructures of γ-GeSe with h-BN/graphene/MoS2

“…In particular, interlayer excitons in vdWHs, providing optically addressable spin and valley degrees of freedom and long lifetimes, 16 have become a research hotspot today. Exciton transistors, 17 exciton routers, 18 moire ´excitons, 19,20 and photo-and electro-luminescence from interlayer excitons 21,22 have been achieved in vdWHs.…”

Giant in-plane optical and electronic anisotropy of tellurene: a quantitative exploration

“…Optical functions, including complex refractive indices and dielectric functions, represent the response of materials to the light and reflect the intrinsic light-matter interactions, [18][19][20] such as interband transition, 21,22 excitonic effect, 23,24 etc. For low-symmetry materials, anisotropic optical functions can be used to quantitatively evaluate and modulate the optically anisotropic phenomena.…”