Mechanisms for intraband energy relaxation in semiconductor quantum dots: The role of electron-hole interactions

Klimov, Victor I.; Mikhailovsky, Alexander; McBranch, D.; Leatherdale, C. A.; Bawendi, Moungi G.

doi:10.1103/physrevb.61.r13349

Cited by 358 publications

(511 citation statements)

References 20 publications

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“…13 A model for MEG in QDs based on the coherent evolution of a single exciton state into multiple exciton states predicts that oscillations (quantum beats) between states of varying numbers of (energy-allowed) exciton states may be observable by ultrafast spectroscopy. 13 While we have not yet obtained unambiguous experimental evidence for such coherent MEG signature oscillations, we demonstrate and describe how the biexciton effect (also known as the transition Stark shift) [14][15][16][17] produces a probe wavelength-dependent transient absorption that complicates the search for coherent oscillations in the ultrafast lowest-exciton bleach signal.…”

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confidence: 87%

“…For such semiconductors with m e * , m h *, Augerlike cooling provides the relaxation route to bypass any phonon bottleneck. 28,29 Inhibiting Auger-like cooling by removing or eliminating one of the carriers required for the Auger process has been shown to result in an approximate 10-fold decrease in the relaxation rate in QDs of CdSe 16,17,30 and InP. 31 However, for PbSe and PbS, the electron and hole effective masses are both (1) relatively small and (2) essentially identical.…”

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confidence: 99%

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Highly Efficient Multiple Exciton Generation in Colloidal PbSe and PbS Quantum Dots

et al. 2005

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We report ultra-efficient multiple exciton generation (MEG) for single photon absorption in colloidal PbSe and PbS quantum dots (QDs). We employ transient absorption spectroscopy and present measurement data acquired for both intraband as well as interband probe energies. Quantum yields of 300% indicate the creation, on average, of three excitons per absorbed photon for PbSe QDs at photon energies that are four times the QD energy gap. Results indicate that the threshold photon energy for MEG in QDs is twice the lowest exciton absorption energy. We find that the biexciton effect, which shifts the transition energy for absorption of a second photon, influences the early time transient absorption data and may contribute to a modulation observed when probing near the lowest interband transition. We present experimental and theoretical values of the size-dependent interband transition energies for PbSe QDs. We present experimental and theoretical values of the size-dependent interband transition energies for PbSe QDs, and we also introduce a new model for MEG based on the coherent superposition of multiple excitonic states.

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confidence: 87%

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confidence: 99%

Highly Efficient Multiple Exciton Generation in Colloidal PbSe and PbS Quantum Dots

et al. 2005

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“…We neglect all extrinsic losses and only take into consideration intrinsic decay channels due to radiative and nonradiative Auger recombinations; the latter process dominates the decay of multi-e-h pairs generated by CM. 10 We first consider the situation without CM. Under solar irradiation, the average number of e-h pairs per NQD, N eh , is less than 0.01 ͑estimated using an upper limit of the NQD absorption cross section of 10 −14 cm 2 ͒, and hence, we can only consider unexcited and singly excited dots and can also neglect multiparticle Auger recombination ͓Fig.…”

Section: Detailed-balance Power Conversion Limits Of Nanocrystal-quanmentioning

confidence: 99%

Detailed-balance power conversion limits of nanocrystal-quantum-dot solar cells in the presence of carrier multiplication

Klimov

2006

Applied Physics Letters

197

161

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Semiconductor nanocrystals can respond to absorption of a single photon by producing multiple electron-hole pairs with extremely high efficiencies. This letter analyzes the impact of this carrier-multiplication (CM) phenomenon on power conversion limits of solar cells using detailed-balance considerations that take into account practical values of CM efficiencies measured in experimental studies. For PbSe nanocrystals that exhibit a ca. 3Eg CM threshold (Eg is the energy gap), the calculated maximum detailed-balance efficiency is 36% in the presence of CM versus 31% in the no-CM case. An increase to 42% is possible if the CM threshold is at its theoretical minimum of 2Eg.

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“…4 These favorable characteristics provide a flexible platform for the development of integrated photonic devices based on NCs, including optical amplifiers and lasers operating at room temperature. The main difficulty in achieving NC-based lasing is the very efficient nonradiative Auger recombination, 5 so that laser operation is achieved so far only with pulsed excitation. 6 Strategies to improve the laser performance are ͑a͒ to increase the NC concentration in the active layer, 7 ͑b͒ the use of high-finesse optical feedback structures, 6 and ͑c͒ the optimization of the optical waveguides.…”

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confidence: 99%

Two- and one-dimensional light propagations and gain in layer-by-layer-deposited colloidal nanocrystal waveguides

Roither¹,

Pichler²,

Kovalenko³

et al. 2006

Applied Physics Letters

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Optical waveguides containing high percentages of colloidal nanocrystals have been fabricated by layer-by-layer deposition on planar and patterned glass substrates. The two-and one-dimensional waveguidings in these structures are demonstrated by propagation loss experiments. The experimental results obtained for various film thicknesses and widths of the waveguide stripes together with simulations of the light propagation indicate that the losses are dominated by surface roughness. The variable stripe length method is used to determine the optical gain of 230 cm −1 from the amplified spontaneous emission. This high value makes the authors' waveguide structures very promising for applications in amplifiers and lasers with reduced threshold powers. 4 These favorable characteristics provide a flexible platform for the development of integrated photonic devices based on NCs, including optical amplifiers and lasers operating at room temperature. The main difficulty in achieving NC-based lasing is the very efficient nonradiative Auger recombination, 5 so that laser operation is achieved so far only with pulsed excitation. 6 Strategies to improve the laser performance are ͑a͒ to increase the NC concentration in the active layer, 7 ͑b͒ the use of high-finesse optical feedback structures, 6 and ͑c͒ the optimization of the optical waveguides. While the properties of optical waveguides containing Si nanocrystals fabricated by implantation have been studied in detail, 8 for waveguides containing colloidal NCs only the principal operation has been demonstrated. 9 Therefore, here we present a systematic investigation of twodimensional ͑2D͒ and one-dimensional ͑1D͒ waveguides ͑WGs͒, optically activated by strongly luminescent colloidal CdTe NCs synthesized according to Ref. 10. To obtain structures with smooth surfaces and high NC volume fractions the layer-by-layer deposition technique 11 is applied. The waveguides exhibit propagation loss coefficients less than 1 cm −1 , depending on the thickness of the WGs. The losses are only weakly dependent on the width of the 1D WGs and are determined by the surface roughness. The amplified spontaneous emission, excited by femtosecond pulses, evidences a high optical gain of 230 cm −1 , showing that our WGs are highly suitable as active components in NC-based lasers and amplifiers.The NC WGs are fabricated by controlled deposition of CdTe NC/polymer films onto glass substrates by the layerby-layer assembly method. 11 This simple technique makes use of the alternating adsorption of ͑sub͒monolayers of oppositely charged molecules or nanoparticles. In particular, we use positively charged poly͑diallyldimethylammonium chloride͒ ͑PDDA͒ molecules in combination with negatively surface-charged CdTe NCs, each provided in aqueous solutions with appropriately adjusted pH values. The total film thickness is controlled by the number of PDDA/CdTe NC bilayers and by the deposition time for each monolayer. For a film with 40 bilayers we obtain a typical thickness of 170 nm. Since the effective thick...

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Mechanisms for intraband energy relaxation in semiconductor quantum dots: The role of electron-hole interactions

Cited by 358 publications

References 20 publications

Highly Efficient Multiple Exciton Generation in Colloidal PbSe and PbS Quantum Dots

Highly Efficient Multiple Exciton Generation in Colloidal PbSe and PbS Quantum Dots

Detailed-balance power conversion limits of nanocrystal-quantum-dot solar cells in the presence of carrier multiplication

Two- and one-dimensional light propagations and gain in layer-by-layer-deposited colloidal nanocrystal waveguides

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