POLARIZED RAMAN-SPECTRA IN GAN

We have measured polarized Raman spectra in a 2.0 mu m GaN epitaxial layer of high quality, grown on a sapphire substrate. All symmetry-allowed optical phonons in GaN have been assigned as follows: A(1)(LO), 735 cm(-1); A(1)(TO), 533 cm(-1). E(1)(LO), 743 cm(-1). E(1)(TO), 561 cm(-1); E(2), 144 and 569 cm(-1). Using the Lyddane-Sachs-Teller relation, the static dielectric constants of GaN for the ordinary and extraordinary directions have been estimated as epsilon(perpendicular to 0) = 9.28 and epsilon(parallel to 0) = 10.1. We have also observed quasi-to phonons in GaN. A brief discussion on these will be given.