Observation of Folded Acoustic Phonons in a Semiconductor Superlattice

Colvard, C.; Merlín, R.; Klein, Miles V.; Gossard, A. C.

doi:10.1103/physrevlett.45.298

Cited by 399 publications

(142 citation statements)

References 12 publications

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“…We recall that the low-frequency zone-center mode possesses the even symmetry A 1 and is, therefore, Raman allowed in the forward scattering geometry [21] whereas its higher-frequency counterpart does not scatter light because its symmetry, B 2 , is odd [12,13]. Furthermore, since the dispersion at is nearly linear, the FP modes behave as weakly-modulated plane waves.…”

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confidence: 99%

“…In layered media, the wavevector-selective acousto-optic mechanism accounts for spontaneous [12,13] and stimulated [14,15] Raman scattering by folded phonons (FP). Our experiments were performed at room temperature using a standard pumpprobe setup in the reflection geometry, in which the only phonons that can be generated or scattered are LA modes propagating along the z-axis [001] [14].…”

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Observation of Surface-Avoiding Waves: A New Class of Extended States in Periodic Media

et al. 2006

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Coherent time-domain optical experiments on GaAs-AlAs superlattices reveal the existence of an unusually long-lived acoustic mode at ~ 0.6 THz, which couples weakly to the environment by evading the sample boundaries. Classical as well as quantum states that steer clear of surfaces are generally shown to occur in the spectrum of periodic structures, for most boundary conditions. These surface-avoiding waves are associated with frequencies outside forbidden gaps and wavevectors in the vicinity of the center and edge of the Brillouin zone. Possible consequences for surface science and resonant cavity applications are discussed.PACS numbers: 43.35.+d, 78.67.Pt, 63.20.-e -1-

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Observation of Surface-Avoiding Waves: A New Class of Extended States in Periodic Media

et al. 2006

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“…Here, light can couple to zone-folded acoustic modes of the superlattice at higher frequencies in the 100 GHz to THz range. These modes have been extensively studied in cw Raman spectroscopy [2][3][4]. The folded bulk acoustic branches are optical branches within the superlattice zone scheme; thus light scattering from those modes is referred to as Raman scattering.…”

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“…Sound velocities and crystal densities are taken from Ref. [2]. In the investigated (001)-oriented samples the ratio of the AlAs layer thickness to the superlattice period x d AlAs ͑͞d GaAs 1 d AlAs ͒ is below 0.55; hence the displacement field of the BZ-center mode on the p 21 branch has A 1 symmetry within the superlattice point group (antisymmetric with respect to a midplane of a layer).…”

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Coherent Zone-Folded Longitudinal Acoustic Phonons in Semiconductor Superlattices: Excitation and Detection

et al. 1999

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Coherent zone-folded acoustic phonons are excited in GaAs͞AlAs superlattices by femtosecond laser pulses via resonant impulsive stimulated Raman scattering in both forward and backward scattering directions. The relative amplitudes of three distinct modes of first and second backfolded order match well with scattering intensities calculated within an elastic continuum model. The detection of the coherent acoustic modes is based on the modulation of the interband transitions via the acoustic deformation potential and exhibits a strong enhancement at interband transitions. [S0031-9007(98)08288-X] PACS numbers: 78.66.Fd, 63.22. + m, 78.47. + p The investigation of low-energy elementary excitations in semiconductor heterostructures is driven by their relevance as the final state in the energy relaxation process. In particular, acoustic phonons play a dominant role for dephasing processes at low lattice temperature and for heat transport in general. Acoustic phonons are commonly investigated by continuous wave (cw) Brillouin scattering. Time resolved experiments based on ultrashort pulse lasers have largely contributed to the understanding of acoustic phonon dynamics. Recently, the generation and propagation of ballistic acoustic phonons in a single semiconductor quantum well was observed by surface deflection spectroscopy [1]. Semiconductor superlattices exhibit zone folding of the acoustic branches within the mini-Brillouinzone (mini-BZ) due to the artificial periodicity of the elastic properties along the growth direction. Here, light can couple to zone-folded acoustic modes of the superlattice at higher frequencies in the 100 GHz to THz range. These modes have been extensively studied in cw Raman spectroscopy [2][3][4]. The folded bulk acoustic branches are optical branches within the superlattice zone scheme; thus light scattering from those modes is referred to as Raman scattering. The coherent excitation of a single first-order zone-folded mode was observed in GaAs͞AlAs superlattices using a time-derivative detection scheme [5]. However, the excitation and detection mechanisms are not yet fully clarified. In this paper we report on the nature of the excitation and detection mechanisms relevant for coherent zone-folded acoustic vibrations of first and second order in GaAs͞AlAs superlattices.Most time resolved experiments on coherent lattice excitations dealt with longitudinal optical phonons [6] or phonon polaritons [7]. While the excitation of phonon polaritons relies on impulsive stimulated Raman scattering (ISRS) [8], in the case of longitudinal optical phonons, a variety of excitation processes have been identified which cannot be explained within the context of stimulated Raman scattering. The most prominent non-Raman type mechanisms are the displacive excitation of coherent phonons relevant for symmetry maintaining optical modes [9] and the generation of coherent LO phonons via rapid surface field screening in polar semiconductors [10]. One important hint towards the determination of the excitation pro...

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“…We assume deformation-potential interaction between the electronic states and the LA vibrations H e-vib = D e͑h͒ ͑zٌ͒ ជ · u ជ m ͑z͒, where D e͑h͒ ͑z͒ is the conduction ͑respectively, valence͒ band deformation potential. [23][24][25][26][27] The sum in Eq. ͑3͒ runs over all intermediate conduction states e and eЈ and initial valence states h. For the sake of simplicity we consider here only zero in-plane wavevector electron-hole transitions.…”

Section: B Quantum Model-raman-brillouin Electronic Densitymentioning

confidence: 99%

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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Observation of Folded Acoustic Phonons in a Semiconductor Superlattice

Cited by 399 publications

References 12 publications

Observation of Surface-Avoiding Waves: A New Class of Extended States in Periodic Media

Observation of Surface-Avoiding Waves: A New Class of Extended States in Periodic Media

Coherent Zone-Folded Longitudinal Acoustic Phonons in Semiconductor Superlattices: Excitation and Detection

Raman-Brillouin electronic density in short-period superlattices

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