GE SEGREGATION TESTED BY X-RAY PHOTOELECTRON DIFFRACTION AND SURFACE ATOM TITRATION DURING THE FIRST STAGE OF SI HETEROEPITAXY ON GE(001)2 X-1

The questions of growth morphology and Ge segregation during Si hetero epitaxial growth on Ge(001)2 x 1 are addressed in the earliest stages of MBE growth (0-3 monolayers) at room temperature (RT) and 400 degree s C using in situ photoemission techniques. X-ray photoelectron diffra ction (XPD) combined with surface atom titration by ultraviolet photoe lectron spectroscopy (UPS), provides a unique way to reach information about the elements (Si or Ge) located in the top layer and their stac king sequences by tracking the appearances of forward scattering event s for different polar directions and Si coverages. The observation of forward scattering reinforcements for the Si2p core level intensity we ll sooner than expected for laminar growth is in favour of Si agglomer ation or (and) Ge segregation, The surface atom titration based on a s elective reactivity of Ge and Si against RT NH3 adsorption shows that at 400 degrees C the surface is essentially Ge terminated and that Ge segregation is prevailing as opposed to the RT growth where Si termina tion prevails. These results are compared to those obtained for the in verted Ge/Si(001) interface.