Phonon dispersion and Raman scattering in hexagonal GaN and AlN

We present the results of room- and low-temperature measurements of second- order Raman scattering for perfect GaN and AlN crystals as well as the Rama n-scattering data for strongly disordered samples. A complete group-theory analysis of phonon symmetry throughout the Brillouin zone and symmetry beha vior of phonon branches, including the analysis of critical points, has bee n performed. The combined treatment of these results and the lattice dynami cal calculations based on the phenomenological interatomic potential model allowed us to obtain the reliable data on the phonon dispersion curves and phonon density-of-states functions in bulk GaN and AlN. [S0163-1829(98)0684 0-4].