Raman spectroscopy has been used to study the zone-folding effects on both longitudinal acoustic (LA) and longitudinal optic (LO) phonons in (GaAs) n -(AlAs) n superlattices with integral n (2 ∼12) grown by molecular-beam epitaxy. All the observed frequencies of the zone-foled LA phonon modes up to the sixth order agree well with those calculated using the elastic model, while the observed frequencies of the zeroth- and first-order zone-folded LO phonon modes agree with those calculated using the linear-chain model. However, since long-range interactions are neglected in the linear-chain model, this model is not a good approximation for the higher-order modes. In contrast to the LA phonon modes, all the GaAs- and AlAs-like LO phonon modes are confined in the GaAs and AlAs layers, respectively.
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Nakayama et al. (1985) studied this question.
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