Quantum dots formed by interface fluctuations in AlAs/GaAs coupled quantum well structures

Zrenner, A.; Butov, L. V.; Hagn, M.; Abstreiter, G.; Böhm, G.; Weimann, G.

doi:10.1103/physrevlett.72.3382

Cited by 313 publications

(141 citation statements)

References 19 publications

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“…The QDs we have studied were formed naturally by interface steps in narrow quantum wells [4][5][6][7]. Specifically, the electrons and holes become localized into QDs in regions of the quantum well that are a monolayer wider than the surrounding region and, therefore, have a slightly smaller confinement energy.…”

Section: Fine Structure Splitting In the Optical Spectra Of Single Gamentioning

confidence: 99%

“…These results are analogous to the early days of atomic spectroscopy as improvements in techniques allowed the observation of fine structure splittings in the optical spectra. However, the physical phenomena responsible for the effects presented here are unique to the quantized condensed matter system.The QDs we have studied were formed naturally by interface steps in narrow quantum wells [4][5][6][7]. Specifically, the electrons and holes become localized into QDs in regions of the quantum well that are a monolayer wider than the surrounding region and, therefore, have a slightly smaller confinement energy.…”

mentioning

confidence: 99%

“…Most previous optical studies of quantum dots (QDs) have probed large ensembles which have led to inhomogeneous broadening of the spectral features. However, recently several groups have shown that it is possible to study single QDs with photoluminescence (PL) either by reducing the size of the sample, [1] by cathodoluminescence [2,3], or by reducing the size of the laser spot on the sample through microscopic [4,5] or optical near-field techniques [6]. Here we use a similar technique whereby we combine high spatial and spectral resolution optics with excitation spectroscopy to study in detail the spectrum of a single QD [7].…”

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Fine Structure Splitting in the Optical Spectra of Single GaAs Quantum Dots

et al. 1996

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We report a photoluminescence study of excitons localized by interface fluctuations in a narrow GaAs͞AlGaAs quantum well. This type of structure provides a valuable system for the optical study of quantum dots. By reducing the area of the sample studied down to the optical near-field regime, only a few dots are probed. With resonant excitation we measure the excited-state spectra of single quantum dots. Many of the spectral lines are linearly polarized with a fine structure splitting of 20 -50 meV. These optical properties are consistent with the characteristic asymmetry of the interface fluctuations. PACS numbers: 78.55.Cr, 71.35.Cc In this Letter we describe the polarization dependence of the optical spectra of single naturally formed GaAs quantum dots. Most previous optical studies of quantum dots (QDs) have probed large ensembles which have led to inhomogeneous broadening of the spectral features. However, recently several groups have shown that it is possible to study single QDs with photoluminescence (PL) either by reducing the size of the sample, [1] by cathodoluminescence [2,3], or by reducing the size of the laser spot on the sample through microscopic [4,5] or optical near-field techniques [6]. Here we use a similar technique whereby we combine high spatial and spectral resolution optics with excitation spectroscopy to study in detail the spectrum of a single QD [7]. With improved resolution we are able to resolve the spectral lines and to study the polarization dependence of the PL spectrum of an individual QD. We often find that the PL is linearly polarized along the (110) crystal axes and observe a fine structure splitting in each of the spectral lines. These results are analogous to the early days of atomic spectroscopy as improvements in techniques allowed the observation of fine structure splittings in the optical spectra. However, the physical phenomena responsible for the effects presented here are unique to the quantized condensed matter system.The QDs we have studied were formed naturally by interface steps in narrow quantum wells [4][5][6][7]. Specifically, the electrons and holes become localized into QDs in regions of the quantum well that are a monolayer wider than the surrounding region and, therefore, have a slightly smaller confinement energy. These well width fluctuations arise from monolayer-high islands at the interfaces which are randomly formed on the growth-interrupted surface by the migration of the cations to step edges. By interrupting the growth these islands can grow to diameters larger than the exciton Bohr diameter (20 nm). A scanning tunneling microscope image of a growth-interrupted GaAs surface grown under similar conditions as our quantum dot sample is shown in Fig. 1. Large monolayer-high islands of varying lateral sizes are evident, and the islands tend to be elongated along the [110] crystal axis. Thus we intuitively expect that the optical properties associated with the localized excitons will reflect this characteristic interface structure. In fact, as we will...

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Section: Fine Structure Splitting In the Optical Spectra Of Single Gamentioning

confidence: 99%

mentioning

confidence: 99%

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confidence: 99%

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Fine Structure Splitting in the Optical Spectra of Single GaAs Quantum Dots

et al. 1996

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“…Luminescence spectra of such systems are known to exhibit a number of intriguing properties which have been interpreted as observation of a precursor of the exciton condensate [1]. Alternatively, they are assigned to effects of trapping of photoexcited carriers in naturally built-in quantum-dot like objects formed by potential fluctuations caused by the interface roughness [2,3].…”

Section: Introductionmentioning

confidence: 99%

Emission from Mesoscopic-Size Islands Formed in a GaAs/AlAs Double Layer Structure

et al. 2004

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The nature of sharp emission lines which are present in macro--luminescence experiments on a type-II GaAs/AlAs double quantum well structure is discussed. The experiments, which also include micro-luminescence measurements, allowed us to conclude that the sharp emission lines observed originate from lateral GaAlAs islands of a few µm in diameter. They serve as efficient type-I recombination centers for indirect excitons and/or carriers which diffuse in the GaAs/AlAs QW structure and strongly affect the emission processes observed in macro-luminescence experiments. These traps can easily be filled with electron-hole pairs, giving rise to the formation of neutral excitons as well as more complex excitonic molecules. Magnetoluminescence spectra from single islands resemble those observed for natural quantum dots formed in narrow GaAs quantum wells.

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“…Over the past 10-15 years two classes of quantum dot structures derived from semiconductor heterostructures have been studied extensively by optical techniques: self-assembled quantum dots produced by the Stranski-Krastanow growth; and so-called interface fluctuation quantum dots [1][2][3][4] produced by interrupted growth at the heterointerfaces of narrow quantum wells. In the former case for structures such as In(Ga)As/GaAs [5], the confinement energies in all three spatial directions typically exceed the electron-hole Coulomb correlation energy (exciton binding energy) of photoexcited electrons and holes by at least an order of magnitude.…”

Section: Introduction/backgroundmentioning

confidence: 99%

Internal Transitions of Charged Excitons in AlGaAs/GaAs Lateral Fluctuation Quantum Dots

et al. 2004

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Low temperature measurements of magneto-photoluminescence and optically detected resonance spectroscopy in magnetic fields up to 10 T were carried out on GaAs/Al 0.3 Ga 0.7 As quantum well samples grown by molecular beam epitaxy with lateral fluctuation quantum dots produced by growth interruption. Monolayer fluctuations of the quantum well width form lateral quantum dots for which confinement energies are less than Coulomb correlation energies. Five different width quantum wells (2.8-14.1 nm) were grown in a single sample, doped in the barriers with Si donors to allow for photoluminescence of both excitons and trions. We report studies of the optically detected resonance spectra associated with the ensemble photoluminescence of all of the wells including observation of bound-to-continuum internal transitions of trions, both singlet and triplet, and electron cyclotron resonance for the wider wells, which also show a clear bound-to-bound triplet transition. The latter is forbidden by magnetic translational invariance, but can be seen in these samples because this symmetry is broken by the lateral fluctuations, whose characteristic dimensions are greater than the trion orbit size. The two narrowest wells show strong broad optically detected resonance signals associated with inhomogeneously broadened internal transitions of the strongly correlated trions in the lateral dots. The optically detected resonance signals peak well below the calculated positions of electron cyclotron resonance. As expected for localized carriers and excitons, there is no free electron cyclotron resonance. We also present preliminary measurements of optically detected resonance spectra from a single dot.

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Quantum dots formed by interface fluctuations in AlAs/GaAs coupled quantum well structures

Cited by 313 publications

References 19 publications

Fine Structure Splitting in the Optical Spectra of Single GaAs Quantum Dots

Fine Structure Splitting in the Optical Spectra of Single GaAs Quantum Dots

Emission from Mesoscopic-Size Islands Formed in a GaAs/AlAs Double Layer Structure

Internal Transitions of Charged Excitons in AlGaAs/GaAs Lateral Fluctuation Quantum Dots

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