Résumé
Highly n-doped InN layers are investigated by means of Raman scattering: a strong mode is evidenced near the frequency of the A1(LO) phonon, despite the high conductivity of the films. This observation is interpreted assuming the breakdown of the wave-vector conservation leading to the decoupling of the plasmon from the phonon. The lineshape of the longitudinal optical mode is simulated using the Lindhard-Mermin dielectric function for various light scattering processes: we found that the charge density fluctuation mechanism is dominant, at least in the visible excitation range.