Folded-acoustic phonons in GaAs/AlAs thin-layer superlattices under high pressure

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Abstract
We have measured the pressure dependence (0–18 GPa) of folded-acoustic-phonon and confined-optic-phonon frequencies in thin-layer GaAs/AlAs superlattices using Raman scattering. The longitudinal-optic phonons of the superlattice increase in frequency with pressure at a rate comparable to that of zone-center optic phonons in bulk materials. For folded-longitudinal-acoustic (LA) phonons we find an increase in frequency, which is consistent with the expected bulk-material behavior under pressure. For superlattices with periods of 41.8 and 20.8 Å the mode Grüneisen parameters are 1.2±0.1 for the folded-LA and confined-optic phonons. These results are discussed relative to bulk and superlattice properties.