Intermixing and buried interfacial structure in strained Ge/Si(105) facets

The strained {105} facet, fundamental in the heteroepitaxial growth of Ge/Si(100), is investigated through a combination of scanning tunneling microscopy, reflectance anisotropy spectroscopy, and density functional theory simulations. Besides providing a strong independent confirmation of the proposed structural model, optical measurements give insight into Si/Ge intermixing, reveal hidden signatures of the buried interface, and give access to a complementary viewpoint of the epitaxial growth with respect to standard top-layer probing. Strained subsurface atoms are found to strongly determine the electronic and optical properties of the whole reconstruction. Moreover, we demonstrate how their unique spectral fingerprint is a sensitive probe of the local chemical bonding environment and allows the stoichiometry of atomic bonds to be monitored within and beneath the surface layer.