Forward Raman scattering by quasilongitudinal optical phonons in GaN

Quasilongitudinal optical phonons in wurtzite GaN have been studied by Rama n spectroscopy in the forward scattering geometry with annular apertures. I t is demonstrated that the geometry is simple and powerful for determining frequency variation of quasilongitudinal optical phonons in a relatively wi de range of their propagation directions, over which the quasilongitudinal optical phonon frequency changes remarkably. Good agreement is obtained bet ween experimental and theoretical results. Discussion is also given on sele ction rules for quasilongitudinal optical phonons, which are used to interp ret polarized Raman signals. (C) 2000 American Institute of Physics. [S0021 -8979(00)06122-3].