Acoustic phonon Raman scattering induced by a built-in electric field

ROZAS G, WINTER MFP, FAINSTEIN A, JUSSERAND B, VACCARO PO, SARAVANAN S

PHYSICAL REVIEW B

AMER PHYSICAL SOC

Año: 2008 vol. 77 p. 1653141 - 1653145

1098-0121

We 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.