ZONE-BOUNDARY PHONONS IN HEXAGONAL AND CUBIC GAN

We present results of second-order Raman-scattering experiments on hex agonal and cubic GaN covering the acoustic and the optical overtone sp ectral region. Based on a comparison of the experimental scattering da ta with the calculated phonon-dispersion curves as well as the group-t heoretically derived selection rules, we were able to assign the obser ved structures to particular phonon branches and determined the points in the Brillouin zone from which the scattering originates. Our measu rements reveal the energies of acoustic zone-boundary phonons in hexag onal GaN.