Control of trion-to-exciton conversion in monolayer WS ₂ by orbital angular momentum of light

Abstract

Controlling the density of exciton and trion quasiparticles in monolayer two-dimensional (2D) materials at room temperature by nondestructive techniques is highly desired for the development of future optoelectronic devices. Here, the effects of different orbital angular momentum (OAM) lights on monolayer tungsten disulfide at both room temperature and low temperatures are investigated, which reveal simultaneously enhanced exciton intensity and suppressed trion intensity in the photoluminescence spectra with increasing topological charge of the OAM light. In addition, the trion-to-exciton conversion efficiency is found to increase rapidly with the OAM light at low laser power and decrease with increasing power. Moreover, the trion binding energy and the concentration of unbound electrons are estimated, which shed light on how these quantities depend on OAM. A phenomenological model is proposed to account for the experimental data. These findings pave a way toward manipulating the exciton emission in 2D materials with OAM light for optoelectronic applications.

Nature of Photoconductivity in Self-Powered Single-Atomic-Layered Nb-Doped WSe2 Phototransistors

“…The deconvoluted PL spectrum of the intrinsic WSe 2 ML (Figure S3) exhibited three peaks at 770, 788, and 814 nm, corresponding to bandgap recombination (exciton recombination), positive trion recombination, and trapping center-related recombination due to the presence of Se vacancy sites, respectively. 33 The deconvoluted PL of the doped ML showed the disappearance of bandgap recombination with a notable enhancement in Se vacancyrelated recombination, which confirmed the introduction of a number of Se vacancies to WSe 2 through Nb doping. 20 Traditionally, asymmetrical MSM photodetectors are constructed with a semiconductor sandwiched between two types of metallic electrodes that form two Schottky contacts with different energy barriers at the metal/semiconductor junctions.…”

Interplay of trapped species and absence of electron capture in Moiré heterobilayers

“…In monolayers with itinerant or defect-localized excitons, at higher laser fluences, the exciton-trion ratio decreases. 35,36,38 This is due to the prevalence of unbound free carriers.…”

“…The strong correlation of the trion PL with the amount of electrostatically doped electrons in the system indicates an absence of trion-exciton conversion at higher excitation fluxes typical of free and trapped intralayer excitons in monolayers. [35][36][37] We note that the absence of optically generated trions is a feature that distinguishes Moiré systems from conventional monolayers that have been studied so far, with itinerant 35,38 or defect-localized intra-layer excitons. 36 The blue shift observed in the PL at lower excitation intensities has been attributed to the dipolar repulsion between interlayer excitons across Moiré trapping sites.…”

Single Photon Emitters with Polarization and Orbital Angular Momentum Locking in Monolayer Semiconductors

“…Recently, there has been growing interest in manipulating excitons in TMD materials with twisted light, − i.e., light carrying nonzero OAM. Here using twisted light in Laguerre–Gaussian (LG) modes with matched OAM, one can directly excite those exciton states with nonzero OAM.…”