Rayleigh acoustic mode in aluminum nitride films

Brillouin light scattering has been used for studying the propagation of the surface Rayleigh mode in AlN films grown by R.F. reactive diode magnetron sputtering on (1-11)-Si substrate. Since the velocity of the shear vertical wave in the film is higher than that in the substrate, the structure is of the type fast film/slow substrate. The evolution of the Rayleigh wave has been analyzed experimentally on films of different thickness between 20 nm and 1.2 μm. The Rayleigh mode exist up to a cutoff value of the ratio h/Λ. For higher values of this parameter this wave becomes a leaky mode radiating energy into the substrate. Measurement of its phase velocity enabled us to determine the value of the effective elastic constant c
₄₄
of the film