Level Repulsion of Localised Excitons Observed in Near-Field Photoluminescence Spectra

Crottini, A.; Kaitouni, R. Idrissi; Staehli, J. L.; Deveaud, B.; Wang, X.L.; Ogura, Mutsuo

doi:10.1002/1521-396x(200204)190:3<631::aid-pssa631>3.0.co;2-v

Cited by 10 publications

(7 citation statements)

References 6 publications

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“…It was concluded that the 3-meV peak in the autocorrelation is not related to level repulsion predicted for a statistical disorder potential with a single correlation length. Recently, autocorrelation spectra from disordered quantum wires 5 have been interpreted as being consistent with the predicted level repulsion scenario.…”

Section: Introductionmentioning

confidence: 67%

“…Recently, there has been considerable experimental [1][2][3][4][5][6][7] and theoretical interest 8,9 in studying the effects of excitonic level repulsion in disordered semiconductor nanostructures, e.g., narrow quantum wells and wires. In such systems, interface roughness and alloy fluctuations on a nanometer scale lead to spatial variations in the effective excitonic center-of-mass potential that tend to localize the excitonic wave functions.…”

Section: Introductionmentioning

confidence: 99%

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Near-field autocorrelation spectroscopy of disordered semiconductor quantum wells

et al. 2004

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Spatially resolved photoluminescence spectra of thin GaAs quantum wells are measured by near-field spectroscopy, and two-energy autocorrelation functions of the spectra are derived. We demonstrate distinctly different autocorrelation functions for a 3-nm-thick quantum well grown on a ͑311͒A surface and for quantum wells grown on ͑100͒ substrates. The autocorrelation spectra of the ͑311͒A GaAs quantum well are quantitatively described by a statistical disorder model with a single correlation length of 17 nm for the exciton center-of-mass motion. A shoulder in the autocorrelation spectrum at energies between 1 and 3 meV is identified as a signature of excitonic level repulsion in the disorder potential. In contrast, the characteristic feature in the autocorrelation spectra of the ͑100͒ quantum wells is an additional positive correlation peak at energies between 3 and 4 meV. This peak reflects the energy correlations between ground and excited exciton states in individual monolayer islands with a narrow size distribution. The results indicate that the disorder potential in these high-quality ͑100͒ GaAs quantum wells contains both contributions from monolayer islands and nanoroughness on a length scale of the exciton Bohr radius.

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Section: Introductionmentioning

confidence: 67%

Section: Introductionmentioning

confidence: 99%

Near-field autocorrelation spectroscopy of disordered semiconductor quantum wells

et al. 2004

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“…We applied the same analysis to our data as that described elsewhere. 11,12,14 The probability to find two exciton emission lines separated energetically by ⌬E is related to the average of the self-convolution of the normalized near-field PL spectra S i (E),…”

Section: B Level Repulsionmentioning

confidence: 99%

“…[11][12][13][14] In all these papers the interpretation of the experimental results is based on numerical solutions of the exciton center-of-mass ͑c.m.͒ Schrödinger equation in a disordered potential with a given correlation length and average potential amplitude. 7,11 The computed exciton eigenstates and energies are used to simulate near-field absorption spectra and their statistical analysis to fit the experiment, tuning the parameters of the potential.…”

Section: Introductionmentioning

confidence: 99%

Exciton relaxation and level repulsion inGaAs/AlxGa1−x
Feltrin
¹
,
Kaitouni
²
,
Crottini
³

et al. 2004
Phys. Rev. B
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V groove GaAs/AlGaAs quantum wires are investigated by spatially resolved photoluminescence spectroscopy using a low-temperature scanning near-field optical microscope. The spectra along the wires feature several sharp emission lines, which are understood as the emission from exciton states localized in inhomogeneities of the confining potential. It is expected that these exciton states spatially overlap and that their energies are correlated, which leads to level repulsion. The statistical analysis of the spectra in terms of autocorrelation functions clearly reveals this effect. In order to model photoluminescence rather than absorption spectra, we perform detailed simulations of exciton relaxation and luminescence kinetics in a disordered one-dimensional system, taking into account the realistic structure of the facets at the bottom of the V groove in our disorder model. Combining near-field measurements and numerical simulations we show that disorder prevents the full relaxation of excitons towards the local ground states in the dips of the disordered potential. As a consequence, luminescence from excited states is observed. We identify in the spatial and energy correlation between localized states the origin of the observed level repulsion and discuss the role played by the two facets at the bottom of the V groove in this mechanism. This analysis also highlights the relevance of the broad photoluminescence background observed in this and in analogous experiments. We propose as explanation for the origin of this broad background the strong exciton-acoustic phonon coupling that results in phonon sidebands in the spectrum of each localized state.

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“…We consider this very strong evidence for quantum mechanical level repulsion in disordered semiconductor nanostructures. Similar conclusions are drawn in a recent investigation of autocorrelation spectra of V-groove QWR [27]. Energ (meV) Fig.…”

Section: Energy (Ev)mentioning

confidence: 99%

Near-Field Spectroscopy of Disordered Nanostructures

Lienau

Intonti

Guenther

et al. 2002

phys. stat. sol. (b)

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Dedicated to Professor Dr. Roland Zimmermann on the occasion of his 60th birthday For many years, Roland Zimmermann and his research group have devoted much of their attention to the effects of disorder and exciton localization on the optical properties of semiconductor nanostructures. With the recent development of spectroscopic techniques providing subwavelength spatial resolution, new experiments became possible to reveal some of the rich physics linked to exciton localization. This paper briefly reviews recent work of the authors' group using near-field nano-spectroscopy. Specifically, it is shown that near-field autocorrelation spectra give strong evidence for quantum mechanical level repulsion of localized exciton states and allow for a quantitative estimate of the underlying microscopic disorder features. Femtosecond non-linear near-field spectroscopy allows to probe the transient optical nonlinearity from a single localized exciton in a thin quantum film on ultrashort time scales.Semiconductor nanostructures are never perfect [1]. Despite the high standard of modern growth techniques, local monolayer height fluctuations at the interfaces (interface roughness) and fluctuations of the alloy composition (alloy disorder) are unavoidable. In quantum wells (QW), this structural disorder gives rise to inhomogeneous broadening of far-field optical spectra, as is well known since more than two decades [2]. Inhomogeneous broadening may be of little importance for thick, high quality quantum wells (Fig. 1). It dominates, however, the linear and nonlinear properties of thin quantum wells, which are often the basis for growth of low-dimensional nanostructures, such as quantum wires and dots. Inhomogeneous broadening is intimately linked to a random spatial localization of electron and hole wave functions within the disordered quantum well and the resulting fluctuations in optical transition energies. This is directly evidenced by recording luminescence spectra with high spatial (<1 mm) and spectral (<0.1 meV) resolution [3][4][5][6]. In such experiments, the smooth far-field PL spectrum breaks up into a series of sharp emission spikes from single localized excitons (Fig. 1).Detailed theoretical investgations in R.Z.'s group [7] suggest that as long as the exciton binding energy is larger or similar to the disorder-induced broadening, the optical properties of such thin quantum wells should follow from solutions of a stationary twodimensional single-exciton Schrö dinger equation. This equation describes the 1s excitonic center-of-mass motion (COM) with an effective disorder potential VðRÞ. VðRÞ is given by the three-dimensional spatial average of the exciton relative wave function over the local band edge fluctuations. This factorization ansatz reduces the numerical analysis of the optical properties of disordered QW to solving of a two-dimensional phys. stat. sol. (b) 234, No. 1, 453-462 (2002)

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Level Repulsion of Localised Excitons Observed in Near-Field Photoluminescence Spectra

Cited by 10 publications

References 6 publications

Near-field autocorrelation spectroscopy of disordered semiconductor quantum wells

Near-field autocorrelation spectroscopy of disordered semiconductor quantum wells

Exciton relaxation and level repulsion inGaAs/AlxGa1−x
Feltrin
¹
,
Kaitouni
²
,
Crottini
³

et al. 2004
Phys. Rev. B
Self Cite
10
0
4
0
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Near-Field Spectroscopy of Disordered Nanostructures

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Level Repulsion of Localised Excitons Observed in Near-Field Photoluminescence Spectra

Cited by 10 publications

References 6 publications

Near-field autocorrelation spectroscopy of disordered semiconductor quantum wells

Near-field autocorrelation spectroscopy of disordered semiconductor quantum wells

Exciton relaxation and level repulsion inGaAs/AlxGa1−xFeltrin1, Kaitouni2, Crottini3 et al. 2004Phys. Rev. BSelf Cite10040View full textAdd to dashboardCite

Near-Field Spectroscopy of Disordered Nanostructures

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Exciton relaxation and level repulsion inGaAs/AlxGa1−x
Feltrin
¹
,
Kaitouni
²
,
Crottini
³

et al. 2004
Phys. Rev. B
Self Cite
10
0
4
0
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