GAN LAYER GROWTH IN RELATION TO BUFFER DEPOSITION TEMPERATURE

Drastic changes in Raman spectra from GaN epitaxial layers are shown t o depend on the GaN buffer layer deposition temperature: for temperatu res higher than 600 degrees C, non intentional n-doping is evidenced b y the screening of the allowed A(1)(LO) phonon by free carriers. Raman measurements at liquid nitrogen temperature confirm this interpretati on and speak in favor oi. degenerate carrier gas. Partial screening of phonons with wave-vectors differing from the q = 0 transfer of. incid ent and scattered photons is invoked to explain LO-like scattering ove r the whole spectral range of optical phonons. Defects correlated to t hree-dimensional growth and to non-radiative recombination processes i n the layers are proposed as the origin of heavy n-doping and of the w ave-vector non-conservation. (C) 1997 Elsevier Science S.A.