POLAR PHONON-INTERSUBBAND PLASMON COUPLING IN SI DELTA-DOPED GAAS

The present work is devoted to Raman scattering by coupled phonon-inte rsubband plasmon excitations in Si delta-doped GaAs. The signature of the coupled modes is pointed out by means of difference Raman scatteri ng, and their symmetry determined according to the selection rules. A good agreement is found between the experimental spectra and those cal culated in the frame of the dielectric response theory. Raman depth pr ofiling measurements have been performed for two locations of the Si-d oped sheet with respect to the sample surface. These results give evid ence for electron localization in the vicinity of the doped sheet and allow the spatial extent of the electron gas to be estimated. The chan ge undergone by the Raman signal of the coupled phonon-plasmon system is studied as a function of doping level, and the ion spreading effect s are discussed. The measurements performed in a wide range of tempera ture are also presented and analyzed.