Light-emitting devices based on atomically thin MoSe_(2)

Atomically thin MoSe_(2) layers,as a core member of the transition metal dichalcogenides(TMDs)family,benefit from their appealing properties,including tunable band gaps,high exciton binding energies,and giant oscillator strengths,thus pro-viding an intriguing platform for optoelectronic applications of light-emitting diodes(LEDs),field-effect transistors(FETs),sin-gle-photon emitters(SPEs),and coherent light sources(CLSs).Moreover,these MoSe_(2) layers can realize strong excitonic emis-sion in the near-infrared wavelengths,which can be combined with the silicon-based integration technologies and further encourage the development of the new generation technologies of on-chip optical interconnection,quantum computing,and quantum information processing.Herein,we overview the state-of-the-art applications of light-emitting devices based on two-dimensional MoSe_(2) layers.Firstly,we introduce recent developments in excitonic emission features from atomically thin MoSe_(2) and their dependences on typical physical fields.Next,we focus on the exciton-polaritons and plasmon-exciton polaritons in MoSe_(2) coupled to the diverse forms of optical microcavities.Then,we highlight the promising applications of LEDs,SPEs,and CLSs based on MoSe_(2) and their heterostructures.Finally,we summarize the challenges and opportunities for high-quality emis-sion of MoSe_(2) and high-performance light-emitting devices.

Probing angle-resolved reflection signatures of intralayer and interlayer excitons in monolayer and bilayer MoS_(2)

Strongly bound excitons in atomically thin transition metal dichalcogenides offer many opportunities to reveal the underlying physics of basic quasiparticles and many-body effects in the two-dimensional(2D)limit.Comprehensive reflection investigation on band-edge exciton transitions is essential to exploring wealthy light–matter interactions in the emerging 2D semiconductors,whereas angle-resolved reflection(ARR)characteristics of intralayer and interlayer excitons in 2D MoS_(2)layers remain unclear.Herein,we report ARR spectroscopic features of A,B,interlayer excitons in monolayer(ML)and bilayer(BL)MoS_(2)on three kinds of photonic substrates,involving distinct exciton–photon interactions.In a BL MoS_(2)on a protected silver mirror,the interlayer exciton with one-third amplitude of A exciton appears at 0.05 eV above the A exciton energy,exhibiting an angleinsensitive energy dispersion.When ML and BL MoS_(2)lie on a SiO_(2)-covered silicon,the broad trapped-photon mode weakly couples with the reflection bands of A and B excitons by the Fano resonance effect,causing the asymmetric lineshapes and the redshifted energies.After transferring MoS_(2)layers onto a one-dimensional photonic crystal,two high-lying branches of B-exciton polaritons are formed by the interactions between B excitons and Bragg photons,beyond the weak-coupling regime.This work provides ARR spectral benchmarks of A,B,interlayer excitons in ML and BL MoS_(2),gaining insights into the interpretation of light–matter interactions in 2D semiconductors and the design of their devices for practical photonic applications.

Monolayer tungsten disulfide in photonic environment:Angleresolved weak and strong light-matter coupling

Light-matter interactions in two-dimensional transition metal dichalcogenides(TMDs)are sensitive to the surrounding dielectric environment.Depending on the interacting strength,weak and strong exciton–photon coupling effects can occur when the exciton energy is resonant with the one of photon.Here we report angle-resolved spectroscopic signatures of monolayer tungsten disulfide(1L-WS2)in weak and strong exciton–photon coupling environments.Inherent optical response of 1L-WS_(2)in the momentum space is uncovered by employing a dielectric mirror as substrate,where the energy dispersion is angleindependent while the amplitudes increase at high detection angles.When 1L-WS_(2)sits on top of a dielectric layer on silicon,the resonant trapped photon weakly couples with the exciton,in which the minimum of reflection dip shifts at both sides of the crossing angle while the emitted exciton energy remains unchanged.The unusual shift of reflection dip is attributed to the presence of Fano resonance under white-light illumination.By embedding 1L-WS_(2)into a dielectric microcavity,strong exciton–photon coupling results in the formation of lower and upper polariton branches with an appreciable Rabi splitting of 34 meV at room temperature,where the observed blueshift of the lower polariton branch is indicative of the enhanced polaritonpolariton scattering.Our findings highlight the effect of dielectric environment on angle-resolved optical response of exciton–photon interactions in a two-dimensional semiconductor,which is helpful to develop practical TMD-based architectures for photonic and polaritonic applications.