Response of the surface dielectric function to dynamic surface modifications: application of reflectance anisotropy spectroscopy and spectroscopic ellipsometry

Both spectroscopic ellipsometry (SE) and reflectance anisotropy spectroscopy (RAS) are able to measure a specific dielectric response of the few uppermost atomic layers of a III-V semiconductor when the surface conditions are changed. The sensitivity of both techniques even under high-temperature epitaxial growth conditions is high enough to follow in situ and on a sub-monolayer scale dynamic surface changes such as desorption/adsorption and roughening/smoothing processes. Here we report on the combined application of RAS and SE for monitoring dynamic changes of the GaAs (001) surface dielectric function during surface treatments under growth conditions in a metal-organic vapor phase epitaxy (MOVPE) reactor. The results are used for the interpretation of the spectral behavior of ellipsometry monolayer oscillations. We conclude that these ellipsometry oscillations during the two-dimensional island growth are caused by periodic surface changes both in morphology and stoichiometry.