Identification of excitons, trions and biexcitons in single-layer WS₂

Abstract

Single-layer WS$_2$ is a direct-gap semiconductor showing strong excitonic photoluminescence features in the visible spectral range. Here, we present temperature-dependent photoluminescence measurements on mechanically exfoliated single-layer WS$_2$, revealing the existence of neutral and charged excitons at low temperatures as well as at room temperature. By applying a gate voltage, we can electrically control the ratio of excitons and trions and assert a residual n-type doping of our samples. At high excitation densities and low temperatures, an additional peak at energies below the trion dominates the photoluminescence, which we identify as biexciton emission.Comment: 6 pages, 5 figure

Exploration of exciton behavior in atomically thin WS2 layers by ionic gating

“…We attribute the peak at 2.022 eV to a superposition of the defect-bound exciton (L 1 ) and biexciton (XX), labeled L 1 /XX, while the peaks below 2 eV correspond to the defect-bound excitons. 7 The presence of these peaks is consistent with previous reports, and the determination of the exciton (X), trion (X-), biexciton (XX), and defect-bound excitons (BX) was confirmed by gatedependent, excitation-intensity-dependent, and helicityresolved PL measurements. 7 To rule out the effects from IL, the PL spectra of both IL and monolayer WS 2 with and without IL have been obtained (see the supplementary material).…”

“…7 The presence of these peaks is consistent with previous reports, and the determination of the exciton (X), trion (X-), biexciton (XX), and defect-bound excitons (BX) was confirmed by gatedependent, excitation-intensity-dependent, and helicityresolved PL measurements. 7 To rule out the effects from IL, the PL spectra of both IL and monolayer WS 2 with and without IL have been obtained (see the supplementary material). In this letter, we focus on the exciton, trion, and biexciton.…”

“…Two-dimensional (2D) transition-metal dichalcogenides (TMDs) are drawing increasing attention for not only their layer-stacking structure and characteristics that resemble those of graphene, 1,2 but also their unique properties, which include thickness-dependent energy band gaps, 3,4 a tightly bound exciton, [5][6][7] an efficiently coupled spin-valley, 8,9 and prominent many-body effects. [10][11][12][13][14][15][16] Thus, 2D TMDs are excellent material candidates for applications in nanoelectronics, optoelectronics, and valleyelectronics, and are also ideal platforms for exploring the physics of 2D materials.…”

“…7,11,[17][18][19][20][21] At a relatively low-level carrier doping obtained by conventional gating at equilibrium, the transitions among exciton, trion, and biexciton, 7,11 a decrease in the exciton binding energy, and the renormalization of a quasiparticle energy bandgap caused by screening the Coulomb interactions were studied. 21 Bandgap renormalization, carrier population inversion, and the absence of exciton peaks were observed in a nonequilibrium state in highly doped mono-and bilayer WS 2 excited by intense optical pump pulses, 22 indicating the emergence of a Mott transition (MT).…”

Defect Healing and Charge Transfer-Mediated Valley Polarization in MoS2/MoSe2/MoS2 Trilayer van der Waals Heterostructures

“…[18][19][20][21][22] Applications require a scalable fabrication platform providing high-quality large-area monolayer TMDC. Unfortunately, the most promising approach today, namely chemical vapor deposition (CVD) growth [23][24][25][26][27] struggles to compete with exfoliated TMDC in terms of sample quality.…”