GaN films of different buffer thicknesses (from 0 to 600 Å) were grown on (0001) sapphire using MOCVD. The epitaxial films show autodoping with carrier concentration ranging from 8x 10^16 to 5x 10^17 cm^-3 as determined by Hall measurements. The Raman scattering reveals that the A1(LO) mode shifts from 733 to 740 cm^-1 as a result of the phonon-plasmon interaction.