UHV-CVD Ge/Si(100) heteroepitaxy monitored by in situ ellipsometry

A low cost ellipsometer based on the four detector photopolarimeter was utilized for in situ monitoring of Ge film deposition on Si. The best fit of the ?-? trajectory, correlated with XPS analysis, allowed to evidence the sensitivity in the sub-monolayer range of this technique. The comparison with results given by complementary analysis techniques showed that the early stage of growth is well monitored by this diagnostics. On the contrary, poor agreement is achieved for thick films, when the micro structure dimensions are no longer negligible with respect to the wavelength and the optical properties of the film cannot be properly described by the effective medium approximation.