ELASTIC CHARACTERIZATION OF A SUPPORTED POROUS SILICON LAYER BY BRILLOUIN-SCATTERING

Brillouin spectroscopy was used to study surface acoustic waves on a s upported layer of (111)-oriented porous silicon having a thickness of 2.7 mu m and a porosity of 30%. The Rayleigh surface wave velocities w ere found to be significantly lower than corresponding velocities for crystalline silicon. A complete set of elastic constants for the porou s layer was determined from the measured directional dependence of the surface wave velocity in the (111) plane. The best-fit constants are C-11=56.0+/-0.7 GPa, C-12=6.7+/-0.3 GPa and C-44=37.0+/-0.8 GPa. The a nisotropy factor, eta=1.50 indicates that the porous layer is elastica lly anisotropic. (C) 1996 American Institute of Physics.