Relaxation Dynamics of Electron–Hole Pairs Studied by Spatiotemporal Pump and Probe Experiments

Große, S.; Arnold, R.C.; Plessen, G. von; Koch, Martin; Feldmann, Jochen; Axt, Vollrath M.; Kuhn, Thomas; Rettig, R.; Stolz, W.

doi:10.1002/1521-3951(199711)204:1<147::aid-pssb147>3.0.co;2-v

Cited by 17 publications

(5 citation statements)

References 11 publications

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“…In the last decade these basic processes in GaAs QWs have attracted continual attention [1][2][3][4][5][6][7][8][9][10][11] . The formation of QW excitons through LO-phonon cascade emission, LA-phonon and carrier-carrier scattering completes within 20 ps after the initial excitation of electronhole pairs 4,7,12 . The created hot QW excitons then thermalize through low-energy acoustic phonon scattering.…”

Section: Introductionmentioning

confidence: 99%

Bose-Einstein statistics in thermalization and photoluminescence of quantum-well excitons

1999

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Quasi-equilibrium relaxational thermodynamics is developed to understand LA-phonon-assisted thermalization of Bose-Einstein distributed excitons in quantum wells. We study the quantumstatistical effects in the relaxational dynamics of the effective temperature of excitons T = T (t). When T is less than the degeneracy temperature T0, well-developed Bose-Einstein statistics of quantum well excitons leads to nonexponential and density-dependent thermalization. At low bath temperatures T b → 0 the thermalization of quantum-statistically degenerate excitons effectively slows down and T (t) ∝ 1/ ln t. We also analyze the optical decay of Bose-Einstein distributed excitons in perfect quantum wells and show how nonclassical statistics influences the effective lifetime τopt. In particular, τopt of a strongly degenerate gas of excitons is given by 2τR, where τR is the intrinsic radiative lifetime of quasi-two-dimensional excitons. Kinetics of resonant photoluminescence of quantum well excitons during their thermalization is studied within the thermodynamic approach and taking into account Bose-Einstein statistics. We find density-dependent photoluminescence dynamics of statistically degenerate excitons. Numerical modeling of the thermalization and photoluminescence kinetics of quasi-two-dimensional excitons are given for GaAs/AlGaAs quantum wells.78. 72.10.Di; 63.20.Kr

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Section: Introductionmentioning

confidence: 99%

Bose-Einstein statistics in thermalization and photoluminescence of quantum-well excitons

1999

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“…In general, systems hosting mobile excitons such as TMDCs fall into two main categories, exhibiting either semiclassical free-particle transport [43][44][45] or hopping between localization sites [46,47]. These mechanisms are typical for Wannier-Mott excitons with spatially extended wave functions in inorganic semiconductors and tightly bound Frenkel-like states in molecular crystals, respectively.…”

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confidence: 99%

Nonclassical Exciton Diffusion in Monolayer WSe2

et al. 2021

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We experimentally demonstrate time-resolved exciton propagation in a monolayer semiconductor at cryogenic temperatures. Monitoring phonon-assisted recombination of dark states, we find a highly unusual case of exciton diffusion. While at 5 K the diffusivity is intrinsically limited by acoustic phonon scattering, we observe a pronounced decrease of the diffusion coefficient with increasing temperature, far below the activation threshold of higher-energy phonon modes. This behavior corresponds neither to wellknown regimes of semiclassical free-particle transport nor to the thermally activated hopping in systems with strong localization. Its origin is discussed in the framework of both microscopic numerical and semiphenomenological analytical models illustrating the observed characteristics of nonclassical propagation. Challenging the established description of mobile excitons in monolayer semiconductors, these results open up avenues to study quantum transport phenomena for excitonic quasiparticles in atomically thin van der Waals materials and their heterostructures.

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“…For cases in which nonlinear decay is relevant, coupling between excited state decay and transport can significantly influence experimental measurements . Treatment of scenarios in which the photogenerated population has not thermalized or is subject to nonlinear recombination will generally require a numerical approach that accounts for the specific scattering and recombination mechanisms relevant to a particular system …”

Section: Methodsmentioning

confidence: 99%

“…20 Treatment of scenarios in which the photogenerated population has not thermalized or is subject to nonlinear recombination will generally require a numerical approach that accounts for the specific scattering and recombination mechanisms relevant to a particular system. 5 To determine a diffusion coefficient with time-resolved microscopy, P ex is imaged by scanning a focused probe over the field of view of the microscope, or alternatively, by using widefield illumination in combination with a two-dimensional detector. 9,10 Mathematically, this operation corresponds to a spatial convolution of the excitation density and the imaged probe beam spatial profile (or equivalently, the point spread function of the microscope).…”

Section: K Rmentioning

confidence: 99%

“…Ultrafast microscopy has emerged as a versatile tool for characterizing the spatial and temporal dynamics of excited states in semiconducting materials. One particularly powerful capability of the technique is direct imaging of excited state spatial evolution on sub-micrometer length scales and sub-picosecond time scales. − By photoexciting a spatially confined excited state population and optically imaging its subsequent spatial evolution, ultrafast microscopy provides the ability to probe excited state transport in a contact-free manner in the bulk − and on nanoscale objects. − The excellent spatial resolution of the technique also provides a means to measure transport in proximity to localized structural or chemical defects so that their impact on bulk properties can be directly probed. − …”

Section: Introductionmentioning

confidence: 99%

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Reduced Artifact Approach for Determining Diffusion Coefficients in Time-Resolved Microscopy

Hickey

Grumstrup

2020

J. Phys. Chem. C

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Ultrafast microscopy methods traditionally assume a Gaussian profile to extract excited state diffusivities from transport measurements. Although this fitting method recovers accurate diffusion coefficients when the point spread function is well-represented by a Gaussian, even minor spatial aberrations introduced by the imaging system cause significant errors in the determined value. To provide a more accurate measure of excited state transport in nano-and microscale materials systems, an alternative analysis protocol is proposed that numerically convolves the Green's function solution to the diffusion equation with the experimentally measured point spread function. In contrast to the Gaussian fitting approach, the numerical convolution is shown to be robust against artifacts caused by nonideal point spread functions. Furthermore, the numerical convolution approach is highly effective at resolving anisotropic diffusion in modeled data.

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Relaxation Dynamics of Electron–Hole Pairs Studied by Spatiotemporal Pump and Probe Experiments

Cited by 17 publications

References 11 publications

Bose-Einstein statistics in thermalization and photoluminescence of quantum-well excitons

Bose-Einstein statistics in thermalization and photoluminescence of quantum-well excitons

Nonclassical Exciton Diffusion in Monolayer WSe2

Reduced Artifact Approach for Determining Diffusion Coefficients in Time-Resolved Microscopy

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