Spontaneous nanostructural island formation and layer-to-island mass transport in Ge layers on Si(111) surfaces

We have deposited Ge on Br-passivated Si(111) surfaces under high vacuum (HV) conditions at room temperature (RT). Ge has grown in a layer-plus-island growth mode. Atomic force microscopy (AFM) measurements on the as-deposited samples show the formation of nanostructural islands. On a 500 °C-annealed sample, the size and the density of islands increase. High resolution X-ray diffraction (HRXRD) and ion channeling experiments show the lack of epitaxial growth. However, Raman spectroscopy measurements show the polycrystallinity of the Ge layer. X-ray reflectivity (XRR) and Raman spectroscopy results show that the Ge/Si interface is sharp for the as-deposited layer and there is no significant intermixing even in the annealed samples. AFM, XRR and Raman spectroscopy results, taken together, indicate mass transport from the Ge layer to Ge islands. The temperature dependence of this mass transfer provides effective activation energy of 0.45±0.04 eV.