RESONANT RAMAN-SCATTERING IN HEXAGONAL GAN

We performed resonant Raman scattering in hexagonal GaN using discrete laser lines in the violet and UV spectral range for optical excitatio n. To tune the energetic position of the fundamental gap E(0) of GaN r elative to the exciting photon energy the sample temperature was varie d between 77 and 870 K. Analyzing both Stokes and anti-Stokes Raman sp ectra, the resonance profiles for Frohlich-induced one-E(1)(LO) and tw o-E(1)(LO) phonon scattering could be deduced, covering the energy ran ge from 0.5 eV below the E(0) gap up to the gap energy. The strength o f deformation-potential scattering by the A(1)(TO) mode was used as an internal reference. For excitation slightly above the E(0) gap energy E(1)(LO) multiphonon scattering up to the fourth order was observed, which reflects the stronger polarity of the Ga-N bond as compared to c onventional III-V semiconductors. (C) 1996 American Institute of Physi cs.