We have studied LO phonon-plasmon coupled modes by means of Raman scattering in n-InP for carrier densities between $6\times {10}^{16}$ and $1\times {10}^{19}$ ${\mathrm{cm}}^{-3}.$ A line-shape theory based on the Lindhard-Mermin dielectric function that takes into account the nonparabolicity of the InP conduction band as well as temperature and finite wave-vector effects is used to fit the Raman spectra and extract accurate values of the electron density. The results obtained from the Lindhard-Mermin model are compared with the charge density determinations based on the Drude and the hydrodynamical models, and the approximations involved in these models are discussed.

• Received 26 February 1999

DOI:https://doi.org/10.1103/PhysRevB.60.5456