Molding 2D Exciton Flux toward Room Temperature Excitonic Devices

Abstract

optoelectronic elements and devices. Owing to the unique talents of electrons and photons, the efficient photonic communication and electronic processing of signals have been proved as the essential and core components the information technology. Electrons as charged particles are sensitive to surroundings because of strong Coulomb interaction, leading to the bottleneck of nanosecond response time for integrated electric devices. The electronic response time and the conversation between photonic and electronic systems inevitably limit the operation speed in the conventional optoelectronic. [1] Thus developing compact photonic devices performing the essential logic operations is promising to accelerate information transmission and processing. In this direction, some simple prototypes, including optoelectronic transistor, compact microring resonator-based modulator, and Mach-Zehnder modulator, have been demonstrated. [2][3][4] The high integration of photonic devices is challenging due to the optical diffraction limit. Although the latter devices have achieved switching speeds exceeding several gigahertz, high packing density is greatly limited by their active-region dimensions of 10-100 µm. Excitons, or bound electron−hole pairs, Devices operating with excitons have promising prospects for overcoming the dilemma of response time and integration in current generation of electron-or/and photon-based elements and devices. In combination with the advantages of emerging twistronics and valleytronics, the atomically thin transition metal dichalcogenide semiconductors open up new opportunities for pursuing practical excitonic devices, where the strong exciton binding energy enables operating exciton at room temperature. The essential and foremost step toward exciton devices is the control of spatiotemporal exciton flux, which is density-dependent and affected by the complex many-body interactions. It can be effectively controlled by the strain, electric field, electron-doping, and local dielectric environment. Intriguingly, exotic phenomena such as exciton condensation, electron-hole liquid, exciton Hall effects, and exciton halo effects can be occurred in 2D exciton system, providing new possibilities for excitonic devices. Up to now, the proof-of-principle of room temperature exciton devices, including excitonic switching and transistor, exciton guides, and excitonic nanolaser, have been realized. Here the authors review the recent advances in molding 2D exciton flux from basic principle, manipulation, exotic phenomena to promising applications and discuss the opportunities and challenges in pushing the frontiers of room temperature excitonic devices.

Surface acoustic wave induced phenomena in two-dimensional materials

“…Electrons play an essential role in transmitting information but suffer from the nanosecond response time owing to the strong Coulomb interaction in opto-electronic devices. 127 Excitons, electron-hole pairs coupled by the Coulomb interaction, are hydrogen-like bosonic quasi-particles (elementary excitation) with a Bohr radius of nanometer dimension and the main quasi-particles mediating the interaction between light and electronic excitations in semiconductors. Excitons can be optically excited and read out, thereby encoding and storing optical signals into excitons' spin, valley, and orbital degrees of freedom.…”

“…The spatial-temporal dynamics of exciton generation, annihilation and spatial diffusion could be separately investigated due to their different time scales. Assuming that none inplane electric field is applied and the many-body interactions between exciton-trion and exciton-phonon could be ignored, the spatial-temporal dynamics of exciton can be written as 127 @Nðr; tÞ…”

“…Owing to the reduced dielectric screenings, enhanced Coulomb interactions, and relatively large effective masses of charge carriers, excitons in 2D TMDC monolayers have a Bohr radius of B1 nm and a binding energy of B500 meV with strong resonances even at room temperature, making them promising for a plethora of optoelectronic and quantum applications. 127 Furthermore, even larger exciton diffusion lengths can be achieved in TMDC-based devices, either by separating electrons and holes in different layers in type-II vdWs heterostructures (where the conduction band minimum and valence band maximum are located in two different layers), [154][155][156][157][158][159] or by using inhomogeneous strain profiles to funnel excitons (i.e. the exciton funneling effect) [133][134][135][136][137] that largely reduce excitonphonon scattering.…”