Raman-scattering spectroscopy has been used to study the folded longitudinal-acoustic (FLA) phonons in three- and four-layer superlattices comprised variously of slabs of GaAs, ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As, and AlAs. For each superlattice, the observed FLA peak frequencies recorded with different exciting wavelengths agree very well with the calculated dispersion relation based on an elastic-continuum model. However, apart from some qualitative trends in the three-layer superlattices, the relative intensities of the Raman FLA peaks are not well reproduced by the photoelastic theory of a perfect superlattice. Reasons for this discrepancy are discussed. The three-layer superlattices exhibited a high photoluminescence efficiency, comparable to that of strained ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$${\mathrm{In}}_{\mathit{x}}$As/GaAs single quantum wells.

• Received 1 February 1993

DOI:https://doi.org/10.1103/PhysRevB.47.13553