Raman study of phonon-plasmon coupling modes in tunnelling GaAs/AlAs superlattices, grown on (311) and (001) surfaces

We have applied the Raman spectroscopy technique to the study of phonon-plasmon coupled modes in Si-doped GaAsn/AlAsm superlattices (SLs), grown on (001), (311)A and (311)B substrates. We have observed the shift and broadening of the Raman peaks in doped SLs, compared with undoped SLs. When the GaAs layers were thinned from 10 to 1 monolayer, the coupled phonon-plasmon modes became three-dimensional-like, and the interaction of plasmons with LO-phonons of AlAs-type took place. The phonon-plasmon interaction of the SLs was numerically simulated. There was a qualitative agreement between the experiment and the calculations. We observed a difference in dispersion between the coupled phonon-plasmon modes for SLs grown on facet surface (311)A and surface (311)B. This is probably due to differences in the electron spectra of such SLs caused by the difference in shape of GaAs quantum objects formed on AlAs reconstructed surfaces.