Direct and Indirect Interlayer Excitons in a van der Waals Heterostructure of hBN/WS₂/MoS₂/hBN

Abstract

A van der Waals (vdW) heterostructure composed of multivalley systems can show excitonic optical responses from interlayer excitons that originate from several valleys in the electronic structure. In this work, we studied photoluminescence (PL) from a vdW heterostructure, WS/MoS, deposited on hexagonal boron nitride (hBN) flakes. PL spectra from the fabricated heterostructures observed at room temperature show PL peaks at 1.3-1.7 eV, which are absent in the PL spectra of WS or MoS monolayers alone. The low-energy PL peaks we observed can be decomposed into three distinct peaks. Through detailed PL measurements and theoretical analysis, including PL imaging, time-resolved PL measurements, and calculation of dielectric function ε(ω) by solving the Bethe-Salpeter equation with G W, we concluded that the three PL peaks originate from direct K-K interlayer excitons, indirect Q-Γ interlayer excitons, and indirect K-Γ interlayer excitons.

Gate-tunable trion switch for excitonic device applications

“…Recently, this problem has been addressed by creating inter-layer exciton [20][21][22][23][24] to suppress the fast radiative decay, and exciton transport over several micrometer in the plane of the layered material has been demonstrated [4]. An external gate control has also been achieved by modulating the binding energy of the neutral exciton [4,5].…”

“…However, controlling these excitonic states electrically remains a challenge due to the charge neutral nature of these excitons. In addition, transport of the exciton also remains challenging due to the ultra-fast radiative recombination of exciton [12][13][14][15][16] resulting from the high oscillator strength [17][18][19] -limiting the application of excitonic devices.Recently, this problem has been addressed by creating inter-layer exciton [20][21][22][23][24] to suppress the fast radiative decay, and exciton transport over several micrometer in the plane of the layered material has been demonstrated [4]. An external gate control has also been achieved by modulating the binding energy of the neutral exciton [4,5].In this regard, the charged exciton or trion (X − ) is promising since its intensity can be readily controlled electrically by modulating the doping density using a gate voltage.…”

Light–matter interaction in van der Waals hetero-structures

“…(d) Room temperature IX photoluminescence spectrum of a hBN encapsulated MoS2/WS2 hetero-bilayer clearly indicating a triplet structure. The individual contributions I1, I2, I3 are included from Voigt fits to the spectrum[95] (similar spectra shown in[55]). (e) DFT band structure of MoS2/WS2 hetero-bilayer with projections of bands onto individual layers are shown with a color gradient showing high degree of hybridization at the Γ and Q/Σ point[95].…”

“…The individual contributions I1, I2, I3 are included from Voigt fits to the spectrum[95] (similar spectra shown in[55]). (e) DFT band structure of MoS2/WS2 hetero-bilayer with projections of bands onto individual layers are shown with a color gradient showing high degree of hybridization at the Γ and Q/Σ point[95]. [(d,e) Reprinted with permission from[95].…”

“…(e) DFT band structure of MoS2/WS2 hetero-bilayer with projections of bands onto individual layers are shown with a color gradient showing high degree of hybridization at the Γ and Q/Σ point[95]. [(d,e) Reprinted with permission from[95]. ]…”