Raman-scattering spectra of coupled LO-phonon–hole-plasmon modes inp-type GaAs

We have measured the room-temperature Raman spectra of the coupled LO-phonon–damped-hole-plasmon modes of ten p-type, Be-doped, molecular-beam-epitaxy-grown GaAs films with hole concentrations from 6.3×${10}^{17}$ to 2.9×${10}^{19}$ ${\mathrm{cm}}^{\mathrm{-}3}$. Although coupled-mode theory predicts the existence of two modes, we observed only one, with an asymmetric line shape. A line-shape analysis combining the deformation-potential and electro-optic mechanisms shows that the theory reproduces the data very well. It also suggests that one mode is suppressed by the large damping of the hole plasmon. The asymmetry of the observed peak is shown to come from interference between Raman scattering from atomic displacement fluctuations and that from macroscopic electric-field fluctuations. The ratio between Hall mobilities of the holes and optical mobilities of the holes from the Raman measurements is ${\mathrm{\mu }}_{\mathrm{Hall}}$/ ${\mathrm{\mu }}_{\mathrm{optical}}$=1.5–2.6 for different hole concentrations.