Probing exciton localization in nonpolar<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">Ga</mml:mi><mml:mi mathvariant="normal">N</mml:mi><mml:mo>∕</mml:mo><mml:mi mathvariant="normal">Al</mml:mi><mml:mi mathvariant="normal">N</mml:mi></mml:mrow></mml:math>quantum dots by single-dot optical spectroscopy

Rol, Fabian; Founta, S.; Mariette, H.; Daudin, B.; Dang, Le Si; Bleuse, J.; Peyrade, D.; Gérard, J. M.; Gayral, B.

doi:10.1103/physrevb.75.125306

Cited by 61 publications

(49 citation statements)

References 33 publications

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“…Our results are in qualitative agreement with the work of Rol et al 30 for GaN QDs, where a similar analysis revealed that the excitons are smaller than the QD size. The extracted quantum efficiency (70 to 80 %) turns out to be lower than that of small In(Ga)As QDs 29 yet larger than the quantum efficiency of large In(Ga)As QDs.…”

supporting

confidence: 93%

Decay dynamics and exciton localization in large GaAs quantum dots grown by droplet epitaxy

et al. 2013

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We investigate the optical emission and decay dynamics of excitons confined in large strain-free GaAs quantum dots grown by droplet epitaxy. From time-resolved measurements combined with a theoretical model we show that droplet-epitaxy quantum dots have a quantum efficiency of about 75 % and an oscillator strength between 8 and 10. The quantum dots are found to be fully described by a model for strongly-confined excitons, in contrast to the theoretical prediction that excitons in large quantum dots exhibit the so-called giant oscillator strength. We attribute these findings to localized ground-state excitons in potential minima created by material intermixing during growth. We provide further evidence for the strong-confinement regime of excitons by extracting the size of electron and hole wavefunctions from the phonon-broadened photoluminescence spectra. Furthermore, we explore the temperature dependence of the decay dynamics and, for some quantum dots, observe a pronounced reduction in the effective transition strength with temperature. We quantify and explain these effects as being an intrinsic property of large quantum dots owing to thermal excitation of the ground-state exciton. Our results provide a detailed understanding of the optical properties of large quantum dots in general, and of quantum dots grown by droplet epitaxy in particular.

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supporting

confidence: 93%

Decay dynamics and exciton localization in large GaAs quantum dots grown by droplet epitaxy

et al. 2013

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“…7), which indicates that potential fluctuations inside the QDs are negligible. This is in contrast with the intra-dot localization reported in the case of nonpolar QDs, 38 which can be attributed to the presence of structural defects. Also in polar InGaN/GaN QDs emitting in the 3.0-2.85 eV spectral range, Lefebvre et al reported carrier localization by potential fluctuations with a spatial extension much smaller than the QD size.…”

Section: Optical Characterizationcontrasting

confidence: 54%

Internal quantum efficiency of III-nitride quantum dot superlattices grown by plasma-assisted molecular-beam epitaxy

Gačević

Das

Teubert

et al. 2011

Journal of Applied Physics

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We present a study of the optical properties of GaN/AlN and InGaN/GaN quantum dot (QD) superlattices grown via plasma-assisted molecular-beam epitaxy, as compared to their quantum well (QW) counterparts. The three-dimensional/two-dimensional nature of the structures has been verified using atomic force microscopy and transmission electron microscopy. The QD superlattices present higher internal quantum efficiency as compared to the respective QWs as a result of the three-dimensional carrier localization in the islands. In the QW samples, photoluminescence (PL) measurements point out a certain degree of carrier localization due to structural defects or thickness fluctuations, which is more pronounced in InGaN/GaN QWs due to alloy inhomogeneity. In the case of the QD stacks, carrier localization on potential fluctuations with a spatial extension smaller than the QD size is observed only for the InGaN QD-sample with the highest In content (peak emission around 2.76 eV). These results confirm the efficiency of the QD three-dimensional confinement in circumventing the potential fluctuations related to structural defects or alloy inhomogeneity. PL excitation measurements demonstrate efficient carrier transfer from the wetting layer to the QDs in the GaN/AlN system, even for low QD densities ($10 10 cm À3). In the case of InGaN/GaN QDs, transport losses in the GaN barriers cannot be discarded, but an upper limit to these losses of 15% is deduced from PL measurements as a function of the excitation wavelength.

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“…The latter process must be efficient to explain the occurrence of intense X emission besides the hybrid-XX emission. Excitonic spin-flip times of QDs in the order of ps have already been reported 48 and acoustic phonon coupling to excitons in GaN/AlN QDs is exceptionally strong 49,50 .…”

Section: Resultsmentioning

confidence: 99%

Manifestation of unconventional biexciton states in quantum dots

et al. 2014

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Although semiconductor excitons consist of a fermionic subsystem (electron and hole), they carry an integer net spin similar to Cooper-electron-pairs. While the latter cause superconductivity by forming a Bose-Einstein-condensate, excitonic condensation is impeded by, for example, a fast radiative decay of the electron-hole pairs. Here, we investigate the behaviour of two electron-hole pairs in a quantum dot with wurtzite crystal structure evoking a charge carrier separation on the basis of large spontaneous and piezoelectric polarizations, thus reducing carrier overlap and consequently decay probabilities. As a direct consequence, we find a hybrid-biexciton complex with a water molecule-like charge distribution enabling anomalous spin configurations. In contrast to the conventional-biexciton complex with a net spin of s ¼ 0, the hybrid-biexciton exhibits s ¼ ± 3, leading to completely different photoluminescence signatures in addition to drastically enhanced charge carrier-binding energies. Consequently, the biexcitonic cascade via the dark exciton can be enhanced on the rise of temperature as approved by photon cross-correlation measurements.

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Probing exciton localization in nonpolarGaN∕AlNquantum dots by single-dot optical spectroscopy

Cited by 61 publications

References 33 publications

Decay dynamics and exciton localization in large GaAs quantum dots grown by droplet epitaxy

Decay dynamics and exciton localization in large GaAs quantum dots grown by droplet epitaxy

Internal quantum efficiency of III-nitride quantum dot superlattices grown by plasma-assisted molecular-beam epitaxy

Manifestation of unconventional biexciton states in quantum dots

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