Enhanced Multiexciton Formation by an Electron-Hole Plasma in 2D Semiconductors

Abstract

Abstract Body: Transition metal dichalcogenide (TMD) semiconductors are layered van der Walls materials that exhibit exceptional optoelectronic properties in monolayer form. Their atomically thin nature and reduced long-range dielectric screening make them ideal systems in which to study many-body electronic states. Notably, excitonic many-body phenomena govern the light-matter interactions in TMD semiconductors and open up new possibilities for novel optoelectronic devices, including new classes of quantum light sources. Thus, understanding the rich suite of many-body phenomena in these systems is motivated by potential applications in on-chip optoelectronics and by the insights that can be gained into the fundamental interactions that govern TMD material properties. Here, the dynamics of several higher-order excitons including trions, biexcitons, and charged biexcitons in monolayer-WSe2 are probed using temperature-, energy-, and power-dependent time-resolved optical spectroscopy. We find that the formation of multiexciton complexes is enhanced by increasing the optical excitation energy for a given density. This enhancement is attributed to formation from an electron-hole plasma which generates 200% more multiexcitons than a lower-energy exciton gas. We further find that the multiexciton enhancement is robust over many samples and diminished with increasing temperature. These studies reveal a complex interplay between the multiexcitons and single-excitons that depends on both the density and excitation energy of the initial exciton population and open new doors to a number of applications such as entangle photon pair production and lasing, highlighting the importance of understanding the formation and relaxation dynamics of the rich manifold of excitons in order to leverage 2D semiconductors for advanced technologies.