Raman spectroscopy of vibrations in superlattices

Jusserand, B.; Cardona, M.

doi:10.1007/bfb0051988

Cited by 189 publications

(141 citation statements)

References 178 publications

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“…4(b), we observe a fair agreement between the data and the calculations for the set of parameters Σ s ∼400 µeV, τ 1 ∼35 ns, τ 2 ∼10 ps, τ 3 ∼6.5 ns, E 1 ∼1 meV, and E 2 ∼20 meV. This latter activation energy is smaller than the characteristic optical phonon energy of 36 meV in bulk GaAs, and this difference may come from strain and confinements effects in the traps formed in the GaAs barrier or in the InAs wetting layer [20]. As far as the carrier dynamics in the traps is concerned, we find that in our experiments performed below 50K, the capture process is dominated by optical phonon emission (τ ↓ ∼τ 2 ).…”

supporting

confidence: 59%

Unconventional motional narrowing in the optical spectrum of a semiconductor quantum dot

et al. 2006

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Motional narrowing refers to the striking phenomenon where the resonance line of a system coupled to a reservoir becomes narrower when increasing the reservoir fluctuation. A textbook example is found in nuclear magnetic resonance, where the fluctuating local magnetic fields created by randomly oriented nuclear spins are averaged when the motion of the nuclei is thermally activated. The existence of a motional narrowing effect in the optical response of semiconductor quantum dots remains so far unexplored. This effect may be important in this instance since the decoherence dynamics is a central issue for the implementation of quantum information processing based on quantum dots. Here we report on the experimental evidence of motional narrowing in the optical spectrum of a semiconductor quantum dot broadened by the spectral diffusion phenomenon. Surprisingly, motional narrowing is achieved when decreasing incident power or temperature, in contrast with the standard phenomenology observed for nuclear magnetic resonance.PACS numbers: 78.67. Hc, 78.55.Cr, In the seminal work on motional narrowing by Bloembergen et al., relaxation effects in nuclear magnetic resonance were beautifully explained by taking into account the influence of the thermal motion of the magnetic nuclei upon the spin-spin interaction [1]. The general treatment of relaxation processes for a system interacting with a reservoir was later formulated by Kubo in a stochastic theory that assumes random perturbations of the system by a fluctuating environment [2]. Depending on the relative magnitude of the spectral modulation amplitude and the inverse of the modulation correlation time, the relaxation dynamics is either in the slow modulation limit, where the optical line-shape reflects directly the statistical distribution of the different system energies, or in the fast modulation limit where the fluctuation is smoothed out and the line-shape is motionally narrowed into a Lorentzian profile. The relevance of motional narrowing for the description of relaxation phenomena has spread throughout many different fields, such as spin relaxation in semiconductors [3], vibrational dephasing in molecular physics [4], or phase noise in optical pumping [5].The optical spectrum of a material system with localized, zero-dimensional electronic states provides a generic example of the influence of a fluctuating environment on the coherence relaxation dynamics. In that case, the perturbing interactions induce a stochastic shift over time of the optical spectrum, resulting in the so-called spectral diffusion effect, which was observed for rare-earth ions [6], molecules [7], or semiconductor quantum dots [8,9]. In this latter system, impurities, defects or localized charges in the vicinity of a quantum dot induce micro-electric fields that shift the quantum dot emission line through the quantum confined Stark effect. The fluctuation of the quantum dot environment thus randomize the emission energy over a spectral range Σ on a characteristic time scale τ c . Spectral dif...

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confidence: 59%

Unconventional motional narrowing in the optical spectrum of a semiconductor quantum dot

et al. 2006

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“…We found, from our band-structure calculations that, according to the GaAs thicknesses, and to the number of periods in the SLs ͑used for the simulations͒, about 4500 electron-hole transitions may significantly contribute to the light-scattering process depending on the considered SL ͑symmetry forbidden transitions such as e 1 -hh 2 , e 1 -lh 2 , e 2 -hh 1 , and e 2 -lh 1 were excluded͒. Since we consider finite superlattices, there is no translational invariance because of the presence of the surface and of the substrate.…”

Section: B Raman-brillouin Electronic Densitymentioning

confidence: 84%

“…Here, we discuss its integral form which has been widely used for the interpretation of the RB scattering in superlattices. 2 For scattering by longitudinal-acoustic ͑LA͒ vibrations, the Raman-Brillouin intensity is given by 2,17,18 I RB ϰ ͯ͵A s…”

Section: A Photoelastic Modelmentioning

confidence: 99%

“…For an infinite superlattice, the dispersion of LA phonons along the superlattice axis is given by the well-known Rytov's formula 2,21 …”

Section: A Photoelastic Modelmentioning

confidence: 99%

“…This topic has been extensively investigated in the past [1][2][3][4][5] and has recently regained a significant interest due to possible generation and detection of high-frequency coherent acoustic waves using femtosecond laser pulses. Applications in vibrational spectroscopy, nanoscale imaging of defects and picosecond modulation of semiconductors optoelectronic properties are targeted.…”

Section: Introductionmentioning

confidence: 99%

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Raman-Brillouin electronic density in short-period superlattices

et al. 2010

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We analyze and interpret resonant Raman-Brillouin scattering by folded acoustic vibrations in short-period GaAs/AlAs superlattices. Analysis of the spectra and their resonance behavior is performed using a RamanBrillouin electronic density constructed by combining thousands transitions between electronic eigenstates of the system according to their weight in the light-scattering process. We show that plots of this effective electronic density allow for capturing the essential physics of the electron-phonon interaction and of the resonant light-scattering process in a situation where complex effects are simultaneously present: electronic confinement in the quantum wells and wave-function delocalization due to interlayer coupling, folding of acoustic dispersion and symmetry changes in the deformation fields, resonant selection of optical transitions. Comparison between the measured spectra and those simulated using the Raman-Brillouin quantum model and the photoelastic model are presented. Activation and/or deactivation of the scattering by acoustic vibration doublets and changes in their intensity ratio with excitation energy are directly related to the Raman-Brillouin electronic density distribution along the superlattices axis. Limitations of the photoelastic model are discussed by comparing the steplike variation in the photoelastic coefficient to the Raman-Brillouin electronic density profiles.

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Piezooptical Properties of GaAs and InP

Theodorou

Tsegas

1999

phys. stat. sol. (b)

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Raman spectroscopy of vibrations in superlattices

Cited by 189 publications

References 178 publications

Unconventional motional narrowing in the optical spectrum of a semiconductor quantum dot

Unconventional motional narrowing in the optical spectrum of a semiconductor quantum dot

Raman-Brillouin electronic density in short-period superlattices

Piezooptical Properties of GaAs and InP

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