RAMAN-STUDY OF LONGITUDINAL OPTICAL PHONON-PLASMON COUPLING AND DISORDER EFFECTS IN HEAVILY BE-DOPED GAAS

Raman spectroscopy measurements have been performed on GaAs:Be samples with high crystalline quality and exceptional heavy doping level ranging from 10(19) to 1.4 X 10(21) cm-3. The recorded spectra show a structure we assigned to a coupled LO phonon-damped plasmon mode. A theoretical expression for the Raman scattering rate by this mode has been derived from a dielectric model and compared to the experimental data. Using a fitting procedure the doping level of the samples has been estimated in agreement with Hall measurements. Moreover, the study of the Raman intensity evolution of both unscreened-LO and coupled phonon-plasmon structures, provided a convenient and rapid method to determine the activated carrier density in p-doped polar semiconductors. Disorder effects due to the dopant impurities have been also observed and analyzed using a spatial correlation model description.