INSITU OPTICAL CHARACTERIZATION WITH MONOLAYER SENSITIVITY - THE AS-TERMINATED SI(111) SURFACE

Silicon wafers capped with a thick amorphous As layer were annealed in a first stage in ultra-high-vacuum (UHV) until all As had desorbed apart from an epitaxial As monolayer. In a second stage then also the monolayer was desorbed by annealing at higher temperatures. These two desorption steps could be repeated by adsorbing again As from an effusion cell on the surface. The desorption and adsorption processes were monitored in situ by spectroscopic ellipsometry (SE) and Raman scattering (RS). The results from ellipsometry spectra reveal differences in the dielectric function for the clean and As-terminated Si(111) surface in the 3 to 4 eV energy range. This is interpreted in terms of electronic interband transitions within the As monolayer bandstructure contributing strongly to the polarizability above 3 eV with maximum slightly above 4 eV. The results show, moreover, that ellipsometry is a very convenient tool for in situ monitoring As adsorption and desorption processes with submonolayer sensitivity.