Lattice dynamics and Raman scattering from GaN:Mn crystals

We are presenting the results of the density functional based calculations of hexagonal GaN:Mn crystal lattice dynamics. Phonon dispersion curves and density of phonon states have been calculated. The phonon density of states has been compared with Raman-scattering spectra. It has been shown that nitrogen vibrations are responsible for the new Raman bands observed at the longitudinal optical phonon spectral region. The Mn vibrations are masked by the strong lattice bands. Investigation of the polarization dependence of Raman intensities enables the determination of symmetries of the phonon bands from the spectral region of longitudinal optical phonons and characteristic for GaN:Mn system. It has been shown that the polarization dependence of the Raman spectra is identical for all these peaks and is characteristic of the bands of A₁ symmetry. The symmetries of the calculated long wavelength phonons are E₁ and A₁. The inconsistency of the experimental results and the results of model calculations suggests an impurity-induced Fr\"ohlich type resonance Raman scattering. This result is supported by the measured dependence of the Raman spectra on excitation laser line. An intermediate energy level of resonance Raman scattering is suggested.