Raman-scattering studies of LO phonons in GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As superlattices

GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As superlattice samples were grown by molecular-beam epitaxy on a [001]-oriented semi-insulating GaAs substrate. Raman spectra of the superlattice structures were measured at room temperature and under off-resonance conditions. The LO phonon modes of GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As superlattices may be divided into three types: AlAs-like LO modes confined in ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As layers, GaAs LO modes confined in GaAs layers, and GaAs-like delocalized modes. In addition to the LO phonons confined in GaAs layers, we have observed AlAs-like LO phonons confined in ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As layers, and present the dispersion curve of AlAs-like LO phonons for bulk ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As.