EFFECT OF SUBSTRATE PHOTOEXCITATION ON THE DYNAMICS OF THE SI-H STRETCH FOR SI(111) H/

The effect of carriers on the dynamics of the Si-H stretch is investig ated. The carriers are generated with 8 ps pulses at 532 nm and the su m-frequency spectrum of the Si-H stretch is then monitored. Modelizati on of the evolution of the carrier density and subsurface temperature provides a quantitative agreement with the variation of intensities an d frequencies of the spectrum. For carrier densities above 0.9 x 10(20 ) cm(-3), a slight reduction of the lifetime of the Si-H stretch is ob served. This is analyzed with a classical image-dipole coupling result ing in an effective distance of 9 Angstrom to the image plane. It also appears that the thermalization occurs faster than 10 ps. This is ana lyzed in terms of a short lifetime (< 10 ps) for the 200 cm(-1) surfac e optical phonon.