Spatiotemporal dynamics of quantum-well excitons

Zhao, Hui; Don, B. Dal; Moehl, S.; Kalt, H.; Ohkawa, Kazuhiro; Hommel, D.

doi:10.1103/physrevb.67.035306

Cited by 45 publications

(37 citation statements)

References 58 publications

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“…Using the correlation length of the interface roughness as the only fitting parameter, the simulation [solid curve in Fig. 1D)] reproduces the experimental result perfectly [8].…”

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confidence: 60%

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Non‐classical excitonic transport in quantum wells

Zhao¹,

Don²,

Moehl³

et al. 2003

Physica Status Solidi (b)

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We report investigations on excitonic transport in ZnSe quantum wells using far-field nano-photoluminescence enhanced by a solid immersion lens. The 250-nm spatial resolution and 5-ps temporal resolution allow the access to non-classical transport regimes. From zero-phonon-line spectroscopy we deduce the spatial distribution of the PL intensity under different cw excitation condition and its temporal evolution after a pulsed excitation, respectively. The periodic quenching of the transport length as function of excitation excess energy and the nonlinear expansion of the PL spot observed in time-resolved experiments reveal the dominance of hot-exciton effects. The experimental data are well modelled by a Monte Carlo simulation. Spatially resolved phonon-sideband spectroscopy is used to observe directly the coherent transport and the energy relaxation of hot excitons during transport. The coherence length is measured to be 300 -400 nm at low temperatures and the excitons are found to remain hot during transport on a length scale of several micrometers. In typical PL experiments, excitons are generated with an excess energy of several tens to several hundreds of meV. Despite the fact that the transport occurs while the excitons are still hot, hot-exciton effects are generally neglected in this kind of studies. In this contribution, we will use the model system ZnSe to point out how hot-exciton effects influence the transport processes in QWs. By nano-PL spectroscopy on both zero-phonon and phonon-assisted recombination, we access the coherent transport regime and monitor the energy relaxation of hot excitons during their real-space transport.

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“…Using the correlation length of the interface roughness as the only fitting parameter, the simulation [solid curve in Fig. 1D)] reproduces the experimental result perfectly [8].…”

supporting

confidence: 60%

“…From the diffusion model, one anticipates a linear increase of the squared FWHM. The observed sub-linear expansion shows again that the diffusion model is not valid for the description of the exciton transport [8].…”

mentioning

confidence: 90%

Non‐classical excitonic transport in quantum wells

Zhao¹,

Don²,

Moehl³

et al. 2003

Physica Status Solidi (b)

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“…Furthermore, this procedure of deducing D a is independent upon the carrier lifetime since the electron-hole recombination only influences the height, not the width, of the profiles. 18 The procedure summarized in Fig. 2 is used to study the ambipolar diffusivity as functions of lattice temperature and carrier density.…”

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confidence: 99%

Temperature dependence of ambipolar diffusion in silicon on insulator

Zhao

2008

Applied Physics Letters

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Spatiotemporal dynamics of electron-hole pairs locally excited in a silicon-on-insulator structure by indirect interband absorption are studied by measuring differential transmission caused by freecarrier absorption of a probe pulse tuned below the bandgap, with 200-fs temporal and 3-µm spatial resolution. From sample temperatures of 250 K to 400 K, the ambipolar diffusivity decreases, and is similar to reported values of bulk silicon. Cooling the sample from 250 K to 90 K, a decrease of ambipolar diffusivity is observed, indicating important influences of defects and residual stress on carrier diffusion. No detectable density dependence of ambipolar diffusivity is observed.

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“…This is due hot excitons in dark states at high momentum, which dominate the early times [7]. We also notice a spatial oscillation of the whole exciton population in the first 50 ps.…”

Section: Non-resonant Excitationmentioning

confidence: 89%

“…2.b., the profile of the PL and the profile of the whole exciton density differ strongly . From [7].…”

Section: Non-resonant Excitationmentioning

confidence: 97%

Spatial breathing of the exciton distribution in ZnSe quantum wells

Don

Zhao

Schwartz

et al. 2004

Physica Status Solidi (b)

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We measured the transport dynamics of excitons in ZnSe quantum wells with help of a time-resolved nanophotoluminescence setup. Right after picosecond excitation, the excitons move out of the laser spot, but then they reverse the direction of propagation, and finally spread out again. We attribute this "spatial breathing" of the exciton population to acoustic phonon emission, which is a predominantly backward scattering event. This permits us to detect the first inelastic scattering event after the fast excitation generation, causing the end of the coherent transport regime. Using this method, we can determine simultaneously the coherence time and length of excitons in an 8nm well to 29 ps and 800 nm, respectively. We can reproduce the results with help of a Monte-Carlo simulation of the exciton dynamics in the well. The obtained values for coherence length and time are consistent with other, independent experiments. 1 Introduction Temporal and spatial coherence are fundamental requirements for coherent manipulation of exciton states and its possible applications like quantum computing. The exciton coherence time can readily be measured e.g. by means of photoluminescence (PL) linewidth [1] or four-wave mixing (FWM) [2] investigations. But studies of the coherence length in the quantum-well plane are much less developed. We present here a new method to measure simultaneously the coherence length and time of excitons in quantum wells. After presenting the samples and the experimental conditions for transport measurements, we will discuss how to deduce the non-classical transport properties of the hot exciton population from the photoluminescence profile. We will support our findings with a Monte-Carlo simulation and finally we will discuss the dependence of the coherence properties on the well width and material system.

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Spatiotemporal dynamics of quantum-well excitons

Cited by 45 publications

References 58 publications

Non‐classical excitonic transport in quantum wells

Non‐classical excitonic transport in quantum wells

Temperature dependence of ambipolar diffusion in silicon on insulator

Spatial breathing of the exciton distribution in ZnSe quantum wells

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