Elastic properties of GaSe films epitaxially grown on the Si(111)1 x 1-H surface, studied by Brillouin scattering

Brillouin light scattering has been used to study the elastic properties of GaSe films of different thicknesses epitaxially grown on a hydrogen-terminated non-reconstructed Si(lll) surface. Both Rayleigh and Sezawa guided acoustic modes have been revealed, and their velocity dispersion measured as a function of the ratio between the film thickness and the acoustic wavelength. This enabled us to determine four of the five GaSe him elastic constants through a non-linear best fit procedure. The fifth elastic constant c(66) was obtained from detection of shear horizontal waves in the thicker film. The results obtained show that the film constants are similar to those of the bulk material, except for the shear elastic constant c(44) which is appreciably lower. The values of the elastic constants thus obtained were used to calculate the Brillouin cross-section taking into account the rippling induced by surface phonons both at the free surface and at the interface. This permitted us to achieve a satisfactory reproduction of the experimental spectra.