Vibrational dephasing dynamics at hydrogenated and deuterated semiconductor surfaces: Symmetry analysis

Raman scattering has been performed on single crystal hydrogenated silicon and germanium surfaces to investigate the temperature dependence of their v ibrational spectral profiles. Based on a single-mode dephasing model for pu re vibrational dephasing, the frequency shift and line broadening were anal yzed to extract the following dephasing parameters: exchange mode frequency , coupling strength, and friction parameter. The exchange modes for the XH stretches on hydrogenated X(100) surfaces (X=Ge, Si, and C) are found to ma tch their respective bending frequencies. The corresponding ones for hydrog enated X(111) surfaces, on the other hand, are located within the bulk phon on. This surface dependence of the exchange mode in surface vibrational dep hasing dynamics is correlated with the structural relaxation and its associ ated symmetry variation at surfaces. It is further confirmed by the experim ents performed on deuterated semiconductor surfaces. A site-symmetry induce d representation method is exploited to analyze the symmetry properties of the surface vibrations on these two surfaces. This group-theoretical analys is has revealed the selection rules of choosing the dominant exchange modes on hydrogenated semiconductor surfaces. We have identified the exchange mo des in the surface phonon spectra of these surfaces according to their symm etry properties. (C) 2000 American Institute of Physics. [S0021-9606(00)701 36-X].