Acoustic barriers and observation of guided elastic waves in GaN-AlN structures by Brillouin scattering - art. no. 205302

We report on the localization of acoustic waves in GaN-AlN heterolayers dep osited on Si that lead to the observation, by Brillouin light scattering, o f distinctive guided excitations associated with the hexagonal (2H) GaN epi layers. These elastic modes include the longitudinal guided resonance (LGR) propagating parallel to the film surface and a shear horizontal resonance (SHR) polarized in the plane of the surface. The observation in light scatt ering of guided excitations arise from the strong elasto-optic properties o f the GaN thin films as well as the presence of AlN that acts as a barrier by reducing energy leakage to the substrate. Calculations of the mode densi ty and displacements disclose characteristics of the LGR and SHR and accoun t for their localization and polarization features. Several of the principa l elastic constants of the GaN layer are determined from the data that also reveal the bulk acoustic phonons and the Rayleigh surface mode.