Electronic Surface Transitions in Si (111) 2×1 Studied by Polarized Light

In the last few years, great attention has been given to the study of electron surface states on clean semiconducturs, Si(111)2×l in particular receiving most of the interest. Despite the great amount of experimental and theoretical work, some controversies still remain to be explained (for example, dynamical LEED data are in disagreement with all the reconstruction models [1]). In order to discriminate between the different models for the reconstruction, we performed measurements of differential reflectivity by means of polarized light. Theoretical calculations [2] based on the selection rules for the optical transitions have been reported in the range 0.3-4.0 eV, where two peaks in ?R/R with unpolarized light occur [3]. Figure 1 shows the spectral dependence of ?R/R for a single domain Si(111)2×l surface with electrical field of light along the [01?1] and [2?11] directions, which in our case, corresponds to the ?J and ?J' lines of the surface Brillouin zone, respectively.