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 molec ular beam epitaxy on Si(001) with Bi as the surfactant were studied with gr azing-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. Withou t a surfactant the critical thickness of Ge/Si(001) is 3 monolayers (ML). U sing 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 grow th. 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. (C) 2000 American Institute of Physics. [S0021-8979(00)07418-1].