Exciton Polarization and Renormalization Effect for Optical Modulation in Monolayer Semiconductors

Abstract

The ideal quantum confinement structure of monolayer semiconductors offers prominent optical modulation capabilities that are mediated by enhanced many-body interactions. Herein, we establish an electrolyte-gating method for tuning the luminescence properties that are in transition metal dichalcogenide (TMDC) monolayers. We fabricate electric double-layer capacitors on TMDC/graphite heterostructures to investigate electric-field- and carrier-density-dependent photoluminescence. The exciton peak energy initially shows a slight quadratic red shift of ∼1 meV without carrier accumulations, which is caused by the quantum-confined Stark effect. In contrast, the exciton resonance exhibits a larger red shift up to 10 meV with the accumulated carrier density above 1013 cm–2. These results indicate that the optical transitions can be largely modulated by the carrier density control in S- and Se-based TMDCs, as triggered by the doping-induced band gap renormalization effect. To further inspire this modulation capability, we also apply our method to electrolyte-based TMDC light-emitting devices. Biasing solely in electrolyte-induced p-i-n junctions yields pronounced red shifts up to 40 meV for exciton and trion electroluminescence. Consequently, our approach reveals that the doping effects in the high-carrier-density regimes are potentially significant for efficient optical modulation in monolayer semiconductors.

Acoustically Driven Stark Effect in Transition Metal Dichalcogenide Monolayers

“…Transition metal dichalcogenide (TMD) monolayers (MLs) are promising material platforms for future optoelectronic applications due to their multiexciton and spin-valley properties. − In order to fulfill the expectations, different approaches have been employed to externally manipulate carriers and the excitonic optical emissions in these systems . External magnetic fields have been largely used to modify electronic and spin-valley properties. − Optical fields − and out-of-plane − electric fields have been employed to tune emission energies via the Stark effect. In-plane electric fields, besides inducing the Stark effect, can be employed to dissociate excitons and induce lateral carrier transport. − Static mechanical strain has also been used to tune emission energies, , induce direct-to-indirect band gap transition, , change the optical response, , and strongly affect carrier dynamics in 2D systems. − The large effective masses and exciton binding energies (compared to III–V semiconductor nanostructures) as well as the strong response to their surroundings are some of the main challenges to achieve on-demand exciton manipulation in TMD MLs. , …”

Anomalous Stark Shift of Excitonic Complexes in Monolayer Semiconductor

“…12,13 The monolayer transition metal dichalcogenides (TMDCs) are atomically thin semiconductors which host strongly bound excitonic complexes, and serve as an excellent test bed for the investigation of QCSE. [14][15][16][17][18][19][20][21] The overall energy shift (∆E) of the exciton peak due to QCSE has two components. A red shift (∆E 1 ) arises due to the opposite movement in energy of the constituent electron state in the conduction band and the hole state in the valence band, and is given by ∆E 1 = −γ F − γ F 2 where F is the electric field along the out of plane direction, γ and γ are respectively the corresponding dipole moment and polarizability.…”

Spatial Control of Dynamic p–i–n Junctions in Transition Metal Dichalcogenide Light-Emitting Devices

“…28 As a result, electroluminescence (EL) is easily generated in electrolyte-based light-emitting devices of both single-crystalline flakes and large-area films, providing a chance for general arguments on the control of light-emitting positions. 12,13,25 In functional optoelectronic devices, fine control of the recombination zone is one of the most important operations because the precise guidance, alignment, and confinement of light ensures device functionality and performance. For example, in order to manipulate the trajectory of light with high precision, some integrated optical devices require light sources to direct light accurately into the waveguides or fibers.…”

“…Atomically thin transition metal dichalcogenides (TMDCs) have garnered significant attention as promising active materials for functional light-emitting device applications owing to their diverse direct bandgaps, − strong quantum confinement, , unique spin-valley coupling, , and robust mechanical flexibility. − In fact, various functional devices have been demonstrated, such as high-performance flexible light-emitting diodes and optical modulators, − quantum and chiral light-emitting devices, − and cavity-integrated photonic devices. , The demonstrated TMDC light-emitting devices are typically categorized into two types: lateral p–i–n diodes (based on the transistor structure) and heterostructured devices. − However, in most TMDC light-emitting devices, the active materials are exfoliated or chemically grown micrometer-scale single-crystalline flakes, which are not suitable for practical applications and integrations. Moreover, although a few large-area TMDC light-emitting devices have been reported, − there is still plenty of room to offer general arguments, among single-crystalline flakes and large-area films, on the fundamental mechanism to determine the recombination zone, which is yet to be elucidated because of their different device structures.…”

“…In such devices, the ion redistribution, solely driven by biasing, induces spontaneous carrier injections and accumulations, resulting in the formation of dynamic p–i–n junction . As a result, electroluminescence (EL) is easily generated in electrolyte-based light-emitting devices of both single-crystalline flakes and large-area films, providing a chance for general arguments on the control of light-emitting positions. ,, …”