THE GE STRANSKI-KRASTANOV GROWTH MODE ON SI(001)(2X1) TESTED BY X-RAYPHOTOELECTRON AND AUGER-ELECTRON DIFFRACTION

X-ray photoelectron and Auger electron diffractions have been used her e for the first time to identify growth morphology in the earliest sta ges (0-10 monolayers) of Ge epitaxy on Si(001)(2 x 1) surfaces held at room temperature (RT) and at 400-degrees-C. The Ge atomic arrangement in the (110BAR) plane is examined by performing polar angle distribut ion of the Ge LMM intensities and by comparison with the corresponding Si2p substrate pattern. A detailed plot as a function of the Ge cover age of the forward scattering peak contrasts in the [111] and [001] di rections, which correspond to the 1st and 3rd atomic neighbour rows, r espectively, yields informations about the layer number distribution a nd the growth mode. Contrarily to the nearly two-dimensional (2D) grow th taking place at RT, we obtain a 3D island formation at 400-degrees- C for a critical thickness exceeding 5 ML. Nevertheless, in the covera ge domain between 2 and 5 ML for which layer-by-layer growth is normal ly expected, the observation of a significant up to 4 ML roughness acr oss the surface prefigurates the islanding process and confirms very r ecent STM reports. Photoelectron scattering results are only consisten t with pure 2D formation during the first 2 ML growth.