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: A₁(LO), 735 cm ^-1; A₁(TO), 533 cm^-1; E₁(LO), 743 cm^-1; E₁(TO), 561 cm^-1; E₂, 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 E/sub //0/=10.1. We have also observed quasi-LO phonons in GaN. A brief discussion on these will be given.