Ultrafast biexciton spectroscopy in semiconductor quantum dots: evidence for early emergence of multiple-exciton generation

Choi, Younghwan; Sim, Sangwan; Lim, Seong Chu; Lee, Young Hee; Choi, Hyunyong

doi:10.1038/srep03206

Cited by 17 publications

(15 citation statements)

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“…When CM occurs, one photoexcited exciton and additionally excited exciton give rise to the formation of biexciton 28,29,35–39 . As the photoexcited carriers increase, a strong local field is developed, consequently predominating a transient Stark shift and a broadened linewidth of absorbance 28,35–38 . Therefore, the presence of biexciton state will be a monitor of CM at above threshold pumping 29,35,37 .…”

Section: Resultsmentioning

confidence: 99%

“…As the photoexcited carriers increase, a strong local field is developed, consequently predominating a transient Stark shift and a broadened linewidth of absorbance 28,35–38 . Therefore, the presence of biexciton state will be a monitor of CM at above threshold pumping 29,35,37 . We compared the pump-excited absorbance spectra for excitation at >2 E g to absorbance spectrum without pumping (Supplementary Fig.…”

Section: Resultsmentioning

confidence: 99%

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Carrier multiplication in van der Waals layered transition metal dichalcogenides

et al. 2019

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Carrier multiplication (CM) is a process in which high-energy free carriers relax by generation of additional electron-hole pairs rather than by heat dissipation. CM is promising disruptive improvements in photovoltaic energy conversion and light detection technologies. Current state-of-the-art nanomaterials including quantum dots and carbon nanotubes have demonstrated CM, but are not satisfactory owing to high-energy-loss and inherent difficulties with carrier extraction. Here, we report CM in van der Waals (vdW) MoTe2 and WSe2 films, and find characteristics, commencing close to the energy conservation limit and reaching up to 99% CM conversion efficiency with the standard model. This is demonstrated by ultrafast optical spectroscopy with independent approaches, photo-induced absorption, photo-induced bleach, and carrier population dynamics. Combined with a high lateral conductivity and an optimal bandgap below 1 eV, these superior CM characteristics identify vdW materials as an attractive candidate material for highly efficient and mechanically flexible solar cells in the future.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Carrier multiplication in van der Waals layered transition metal dichalcogenides

et al. 2019

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“…The prominence of such four-body correlated states in the material reflects the unusual strength of many-body interactions in atomically thin TMDC semiconductors. Monolayer TMDC materials are thus very favourable candidates for other many-body processes, such as multiple-exciton generation 37 , and for the creation of new higher-order correlated states, such as exciton condensates or the recently introduced dropletons 8 . The existence of the degenerate K and K valleys also offers the possibility of creating optically bright biexciton states with pairs of carriers in distinct valleys.…”

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confidence: 99%

Observation of biexcitons in monolayer WSe2

et al. 2015

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Transition metal dichalcogenide (TMDC) crystals exhibit new emergent properties at monolayer thickness 1,2 , notably strong many-body e ects mediated by Coulomb interactions 3-6. A manifestation of these many-body interactions is the formation of excitons, bound electron-hole pairs, but higher-order excitonic states are also possible. Here we demonstrate the existence of four-body, biexciton states in monolayer WSe 2. The biexciton is identified as a sharply defined state in photoluminescence at high exciton density. Its binding energy of 52 meV is more than an order of magnitude greater than that found in conventional quantum-well structures 7. A variational calculation of the biexciton state reveals that the high binding energy arises not only from strong carrier confinement, but also from reduced and non-local dielectric screening. These results open the way for the creation of new correlated excitonic states linking the degenerate valleys in TMDC crystals, as well as more complex many-body states such as exciton condensates or the recently reported dropletons 8. TMDC crystals, including MoS 2 , MoSe 2 , WS 2 and WSe 2 , are semiconductors that form layered structures with a plane of hexagonal metal atoms surrounded by two planes of chalcogen atoms in trigonal prismatic coordination. At monolayer thickness, these crystals exhibit direct band gaps at the K and K points in the Brillouin zone 1,2 , and recent studies have revealed the possibility of selectively accessing the K or K valley through the use of circularly polarized light 9-12 , as well as the existence of an associated valley Hall effect 13. Importantly, many-body Coulomb interactions in these monolayer TMDC crystals have been found to be particularly strong. This leads to excitonic optical transitions in the materials, with exciton binding energies of several hundred meV (refs 3-6). In the presence of free charges, stable charged excitons (trions) have also been identified and exhibit binding energies of tens of meV (refs 12,14-16). In view of the prominence of these two-and three-body excitonic states, it is natural to ask whether two-dimensional (2D) TMDC materials, just as for the much-studied zero-and one-dimensional nanostructures 7,17-21 , also support the formation of stable biexcitons 22,23. Here we demonstrate the presence of biexcitons in monolayer WSe 2 through the discovery of a sharp new emission peak under pulsed laser excitation. We further probe the properties of the biexciton state through measurements of its ultrafast dynamics, valley polarization and thermal stability. We establish a biexciton binding energy of 52 meV. This unusually high binding energy is compatible with results of a variational analysis of biexcitonic states performed using a non-locally screened Coulomb potential to describe the interactions of charges in the atomically thin 2D material.

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“…The inherent advantages of high quantum efficiency and short lifetime present in colloidal QDs could potentially open up a plethora of opportunities in the field of high-speed OWC systems, such as the phosphor-based transmitter [19] and receiver modules [20] as demonstrated in our prior works. In this regard, the colloidal lead sulphide (PbS) QDs, could be a promising candidate due to their broad absorption range from ultraviolet (UV) to NIR and possibility to control the emission wavelength in the NIR range simply by tuning the QDs diameters [21]. Moreover, the solutionprocessed QDs can be easily integrated as the color-converting components by facile and standard fabrication techniques, e.g.…”

Section: Introductionmentioning

confidence: 99%

Colloidal PbS Quantum Dots for Visible-to-Near-Infrared Optical Internet of Things

et al. 2021

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The emergence of optical Internet of Things (optical-IoT) for sixth-generation (6G) networks has been envisaged to relieve the bandwidth congestion in the conventional radio frequency (RF) channel, and to support the ever-increasing number of smart devices. Among the plethora of device innovations deemed essential for fortifying the development, herein we report on the visible-to-near-infrared colorconversion luminescent-dyes based on lead sulphide quantum dots (PbS QDs), so as to achieve an eyesafe high-speed optical link. The solution-processed PbS QDs exhibited strong absorption in the visible range, radiative recombination lifetime of 6.4 μs, as well as high photoluminescence quantum yield of up to 88%. Our proof-of-principle demonstration based on an orthogonal frequency-division multiplexing (OFDM) modulation scheme established an infrared data transmission of 0.27 Mbit/s, readily supporting an indoor optical-IoT system, and shed light on the possibility for PbS-integrated transceivers in supporting remote access control of multiple nodes. We further envisaged that our investigations could find applications in future development of solution-processable PbS-integrated luminescent fibers, concentrators, and waveguides for high-speed optical receivers.

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Ultrafast biexciton spectroscopy in semiconductor quantum dots: evidence for early emergence of multiple-exciton generation

Cited by 17 publications

References 50 publications

Carrier multiplication in van der Waals layered transition metal dichalcogenides

Carrier multiplication in van der Waals layered transition metal dichalcogenides

Observation of biexcitons in monolayer WSe2

Colloidal PbS Quantum Dots for Visible-to-Near-Infrared Optical Internet of Things

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