Near edge X-ray absorption and X-ray photoelectron diffraction studies of the structural environment of Ge-Si systems

Near edge X-ray absorption spectroscopy (XAS), X-ray photoelectron diffract ion (XPD) and Auger electron diffraction (AED) are powerful techniques for the qualitative study of the structural and electronic properties of severa l systems. The recent development of a multiple scattering approach to simu lating experimental spectra opened a friendly way to the study of structura l environments of solids and surfaces. This article reviews recent X-ray ab sorption experiments using synchrotron radiation which were performed at Ge L edges and core level electron diffraction measurements obtained using a traditional X-ray source from Ge core levels for ultrathin Ge films deposit ed on silicon substrates. Thermodynamics and surface reconstruction have be en found to play a crucial role in the first stages of Ge growth on Si(001) and Si(111) surfaces. Both techniques show the occurrence of intermixing p rocesses even for room-temperature-grown Ge/Si(001) samples and give a stra ightforward measurement of the overlayer tetragonal distortion. The effects of Sb as a surfactant on the Ge/Si(001) interface have also been investiga ted. In this case, evidence of layer-by-layer growth of the fully strained Ge overlayer with a reduced intermixing is obtained when one monolayer of S b is predeposited on the surface.