Intrinsic mechanism for the poor luminescence properties of quantum-box systems

Benisty, H.; Sotomayor-Torres, C M; Weisbuch, C.

doi:10.1103/physrevb.44.10945

Cited by 869 publications

(394 citation statements)

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“…10 In the present work we observe clear phonon suppression in n-type quasi 0D dots ͑i.e., Landau quantized rather than spatially quantized͒ by a time-resolved intraband absorption measurement. This provides unambiguous evidence for the phonon bottleneck effect independently of arguments concerning which processes dominate in the interband photoluminescence measurements in dots [3][4][5][6][9][10][11][12] and quasi dots 13 such as electron-hole scattering. Further, because of the very clean model system ͑much sharper interfaces and no wetting layer, etc.͒, the interpretation is not complicated by detailed questions about different growth techniques and the quality of different dot sample structures.…”

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confidence: 73%

“…Recently much work has been carried out on the so-called ''phonon bottleneck'' that has been claimed to inhibit the cooling of carriers in quantum dots when the level separation is not equal to the phonon energy. [2][3][4][5][6] However, partly as a result of different groups using different growth techniques for interband photoluminescence samples and partly on fundamental grounds, this is controversial and is the subject of much debate. [7][8][9][10][11][12] Indeed several mechanisms have been proposed that may bypass the bottleneck, such as multiphonon scattering, 7 Auger processes, 8 excitonic effects, 9 and defect related processes.…”

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confidence: 99%

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Suppression of LO phonon scattering in Landau quantized quantum dots

et al. 1999

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Picosecond time-resolved far-infrared measurements are presented of the scattering between conductionband states in a doped quasi quantum dot. These states are created by the application of a magnetic field along the growth direction of an InAs/AlSb quantum well. A clear suppression of the cooling rate is seen, from 10 12 s Ϫ1 when the level spacing is equal to the phonon energy, to 10 10 s Ϫ1 away from this resonance, and thus the results provide unambiguous evidence for the phonon bottleneck. Furthermore, the lifetimes had only weak dependence on temperature between 4 and 80 K. ͓S0163-1829͑99͒50612-7͔Electronic lifetimes of two-dimensional ͑2D͒ systems in magnetic fields are of fundamental interest in part because the quantization effect of the magnetic field mimics the effect of a quantum dot potential with an easily variable degree of confinement. 1 The magnetic field perpendicular to the layers forces the electrons into confined orbits and the density of states becomes a ladder of broadened ␦ functions similar to that of a quantum dot. Recently much work has been carried out on the so-called ''phonon bottleneck'' that has been claimed to inhibit the cooling of carriers in quantum dots when the level separation is not equal to the phonon energy. [2][3][4][5][6] However, partly as a result of different groups using different growth techniques for interband photoluminescence samples and partly on fundamental grounds, this is controversial and is the subject of much debate. 7-12 Indeed several mechanisms have been proposed that may bypass the bottleneck, such as multiphonon scattering, 7 Auger processes, 8 excitonic effects, 9 and defect related processes. 10 In the present work we observe clear phonon suppression in n-type quasi 0D dots ͑i.e., Landau quantized rather than spatially quantized͒ by a time-resolved intraband absorption measurement. This provides unambiguous evidence for the phonon bottleneck effect independently of arguments concerning which processes dominate in the interband photoluminescence measurements in dots 3-6,9-12 and quasi dots 13 such as electron-hole scattering. Further, because of the very clean model system ͑much sharper interfaces and no wetting layer, etc.͒, the interpretation is not complicated by detailed questions about different growth techniques and the quality of different dot sample structures. The results should assist in the understanding of which aspect of these processes is fundamental and which is dependent on sample structure.Resonant absorption of longitudinal optic ͑LO͒ phonons causes a variety of transport properties to oscillate with applied magnetic field, such as the magnetoresistance. 14 Resonant phonon scattering occurs whenwhere ប LO is the LO phonon energy, ប c ϭបeB/m* is the cyclotron energy, and ⌬l is an integer. At these resonances the LO phonon absorption/emission probability is strongly enhanced giving rise to large changes in the electron energy relaxation lifetime. 15,16 In the present work we have used the pump-probe technique, with cyclotron resonan...

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Suppression of LO phonon scattering in Landau quantized quantum dots

et al. 1999

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“…Examples include the expected extension of radiative intraband emission far into the mid-IR [3], or the utilization of the excess energy ∆ excess to create additional electronhole pairs [4]. This phonon-bottleneck scenario [5,6] was postulated on the basis that quantum confinement in zero-dimensional nanostructures increases the spacing between electronic energy levels, while leaving the phonon energies largely unchanged. Indeed, in CdSe [7] and PbSe [8][9][10] nanocrystals, the spacing between the first and second electron levels (S and P in Fig.…”

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Excited-state relaxation in PbSe quantum dots

Califano²,

Franceschetti³

et al. 2008

The Journal of Chemical Physics

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While in solids the phonon-assisted, non-radiative decay from high-energy excited states to lowenergy excited states is picosecond fast, it was hoped that electron and hole relaxation could be slowed down in quantum dots, due to the unavailability of phonons energy-matched to the large energy-level spacings ("phonon-bottleneck"). However, excited-state relaxation was observed to be rather fast (≤ 1 ps) in InP, CdSe, and ZnO dots, and explained by an efficient Auger mechanism, whereby the excess energy of electrons is transferred non-radiatively to holes, which can then decay rapidly by phonon emission, by virtue of the densely spaced valence-band levels. The recent emergence of PbSe as a novel quantum-dot material has rekindled the hope for a slow-down of excited-state relaxation, because hole relaxation was deemed to be ineffective on account of the widely spaced hole levels. The assumption of sparse hole energy levels in PbSe was based on an effective-mass argument based on the light effective mass of the hole. Surprisingly, fast intraband relaxation times of 1 to 7 ps were observed in PbSe quantum dots, and have been considered contradictory with the Auger cooling mechanism, because of the assumed sparsity of the hole energy levels. Our pseudopotential calculations, however, do not support the scenario of sparse hole levels in PbSe: Because of the existence of three valence-band maxima in the bulk PbSe band structure, hole energy levels are densely spaced, in contradiction with simple effective-mass models. The remaining question is whether the Auger decay channel is sufficiently fast to account for the fast intraband relaxation. Using the atomistic pseudopotential wave functions of Pb2046Se2117 and Pb260Se249 quantum-dots, we calculated explicitly the electron-hole Coulomb integrals and the P→S electron Auger relaxation rate. We find that the Auger mechanism can explain the experimentally observed P→S intraband decay time scale without the need to invoke any exotic relaxation mechanisms.PACS numbers:

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“…Reduction of the phonon bottleneck by defect assisted phonon emission has been proposed 19 as a mechanism to explain the bright PL emission in QDs. Introduction of deep level defects as those originated from displacement damage might provide additional relaxation paths 20 for thermalization of carriers and therefore increase the luminescence emission.…”

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confidence: 99%