X-ray scattering studies of surfactant mediated epitaxial growth of Si/Ge/Si(001) heterostructures

The strain and morphology of Si/Ge films grown by surfactant mediated molecular beam epitaxy on Si(001) with Bi as the surfactant were studied with grazing-incidence x-ray diffraction, x-ray reflectivity, low-energy electron diffraction, and Auger electron spectroscopy. Bi is observed to prevent the intermixing of Ge and Si layers by inhibiting Ge segregation in Si. Without a surfactant the critical thickness of Ge/Si(001) is 3 monolayers (ML). Using Bi, two-dimensional growth of Ge is observed for films up to 10 ML in thickness, with the onset of strain relaxation occurring at 7 ML of Ge growth. At 10 ML, the top Ge atomic layers are only partially relaxed. This is achieved by introducing roughness at the interface of the Ge and Si layers.