Excitonic Lasers In Atomically Thin 2d Semiconductors

Two-dimensional (2D) atomically thin transition-metal dichalcogenides (TMD) and their van der Waals (vdW) heterostructures offer a platform with tightly bound intralayer/interlayer excitons for the on-chip fabrication of ultracompact nanolasers. Excitons in 2D TMD materials present a considerable binding energy of up to hundreds of meV, which permits a high Mott transition density of 10(14) cm(-2) and stable excitonic lasing under room-temperature operation and high pump fluences. Here, we review the recent progress on the lasing emission from intralayer excitons in TMD monolayers and interlayer excitons in vdW heterostructures incorporated with various high-quality optical cavities, including photonic-crystal, whispering-gallery-mode, distributed-feedback, distributed-Bragg-reflector cavities. Lasing emissions in TMD monolayers and heterostructures have been demonstrated by narrow emission peaks, a clear threshold for nonlinear amplification, time- and spatial coherence under either continuous-wave or pulsed light pumping. Finally, prospective and frontier research topics, including large-scale on-chip integration of TMD nanolasers, electrically pumped lasers, spin-polarized nanolasers, and exciton-polariton Bose-Einstein condensation (BEC) are highlighted.