Raman study of collective plasmon-longitudinal optical phonon excitations in cubic GaN and Al_xGa_1-xN epitaxial layers

The plasmon-longitudinal optical (LO) phonon collective excitations were studied by Raman scattering in cubic GaN doped with Si and in intrinsically doped cubic Al_xGa_1-xN alloys. The specific asymmetry of the corresponding Raman lines, associated with the dispersion of the coupled excitations was clearly detected in GaN. The spatial coherence of the relevant coupled oscillations was determined from the comparison of the experimental Raman spectra with the calculated ones. A broad line, which was previously attributed to the overdamped plasmon-LO phonon oscillations, was also observed in the GaN and Al_xGa_1-xN samples in the range between the transversal optical and LO phonon frequencies. © 2002 American Institute of Physics.