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 heteroepitaxial 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 degrees C using in situ photoemission techniques. X-ray photoelectron diffraction (XPD) combined with surface atom titration by ultraviolet photoelectron spectroscopy (UPS), provides a unique way to reach information about the elements (Si or Ge) located in the top layer and their stacking sequences by tracking the appearances of forward scattering events for different polar directions and Si coverages. The observation of forward scattering reinforcements for the Si2p core level intensity well sooner than expected for laminar growth is in favour of Si agglomeration or (and) Ge segregation, The surface atom titration based on a selective 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 termination prevails. These results are compared to those obtained for the inverted Ge/Si(001) interface.