Surface segregation of Ge during Si growth on Ge/Si(0 0 1) at low temperature observed by high-resolution RBS

The Si/Ge/Si(0 0 1) multilayer with about 1 ML Ge layer is fabricated by evaporating Si overlayer on a Ge/Si(0 0 1) surface at 20-300 °C. The depth profile of the Ge atoms is observed by high-resolution Rutherford backscattering spectroscopy to investigate the possibility of Ge delta doping in Si. The observed profile of the Ge atoms spreads over several atomic layers even at 20 °C and a significant amount of Ge is located in the surface layer at higher temperatures. The results at 20-150 °C are well explained with two-layer model for surface segregation of the Ge atoms and the segregation rates are estimated. The activation energy for surface segregation of Ge atoms in amorphous Si is evaluated to be 0.035 eV, which is much smaller than the value reported for Si deposition at 500 °C. The small activation energy suggests that local heating during the Si deposition is dominant at low temperature.