Resonant Raman studies of confined LO modes and interface modes in a small-period GaAs/AlAs superlattice

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Abstract
Resonant Raman scattering has been used to study the confined LO modes and interface modes near the lowest direct band gap of a GaAs/AlAs superlattice. We have studied the polarization dependence of the resonance profiles in detail. The peak positions of the polarized and depolarized resonance profiles are not the same. When the laser is polarized along (110) or (11¯0), we see an interference effect for some of these modes similar to that seen by Menéndez and Cardona in bulk GaAs. In bulk GaAs, this interference is an intrinsic effect. In superlattices, this effect is a violation of the selection rules for confined LO modes; we attribute this ‘‘forbidden’’ scattering by confined LO modes to an impurity-induced Fröhlich mechanism.