Femtosecond pump-probe experiments on a Ga0.85In0.15As nanocavity enclosed by two Ga(0.85)In(0.15)As/AlAs phonon Bragg mirrors reveal selective generation of terahertz confined acoustic modes and regular folded phonons. Selective generation of the confined modes alone is achievable for laser excitation at certain energies below the mirror absorption edges, corresponding to electronic transitions within the cavity layer only. Calculations based on the photoelastic effect explain the experimental results. Decay times of cavity and regular modes evidence longer decay times and anharmonic effects for the cavity mode.

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We describe semiconductor cavities based on strained Ga0.85In0.15As/AlAs multilayers with permanent built-in piezoelectric fields that confine acoustic phonons in the THz range. The possible role of piezoelectric fields on the phonon lifetimes and on Raman scattering is discussed. Phonon mirrors and cavities grown along [001] (non-piezoelectric) and along [311] (piezoelectric) are studied and compared using high-resolution Raman spectra and photoelastic model calculations. The high quality of the grown [001]([311]) structures is demonstrated by the observation of up to 7(5) orders of folded acoustic phonons and the excellent agreement with theory. We observe a large broadening of the acoustic phonon peaks in the piezoelectric [311] structures upon carrier injection with near-gap excitation. Such acoustic phonon lifetime reduction evidences a strongly modified electron-acoustic phonon interaction in these structures

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International audienceWe report acoustic phonon resonant Raman scattering experiments in strained piezoelectric [311] Ga0.85In0.15As/AlAs superlattices with permanent built-in piezoelectric fields. The acoustic phonon spectra develop upon resonant excitation around the ``forbidden'' hh(2) -> e(1) interband transition into a broad intense structure, which is peaked at the first folded phonons. Standard narrow acoustic phonon doublets are recovered when the power of the resonant laser excitation is increased. Such change in the resonant Raman spectra with increasing power is accompanied by a strong shift and bleaching of a photoluminescence emission related to the hh(2) -> e(1) transition. None of these observations are present in [001] Ga0.85In0.15As/AlAs superlattices that lack the built-in fields because of symmetry. We interpret these results as originated in a Raman process resonant with an intermediate transition that becomes allowed due to the built-in fields. We address the possible mechanisms by which the acoustic phonons strongly modulate the dielectric function in these piezoelectric nanostrutures, including an electron-acoustic-phonon interaction involving the phonon modulation of the built-in fields. This mechanism, which is shown to be proportional to the magnitude of the built-in fields, is quenched when the latter are screened by photoexcited carriers