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Romain Dujardin

Molecular beam epitaxy of isolated germanium nanostrutures on silicon

Published on 11 December 2006
Thesis presented December 11, 2006

The works presented in this manuscript focus on the growth by molecular beam epitaxy (MBE) of Ge isolated nanostructures on Si. Growth of high density isolated Ge dots through a very thin silicon oxide layer, self organized Ge dots on Si islands and Ge nanostructures incorporated in Si nanowires have been investigated. Investigations of the structural properties of ultra small Ge dots, grown through a thin silicon oxide layer on Si(001), have been performed by combining Grazing Incidence X-ray Diffraction (GID) and Surface Extended X-ray Absorption Fine Structure (SEXAFS). Dots are highly strained to the Si (001) substrate and are almost pure Ge. Structural properties of these dots embedded into Si have been investigated by High Resolution Transmission Electron Microscopy (HRTEM). Low temperature photoluminescence studies evidenced a visible luminescence, induced by the presence of Ge-O bonds. These bonds have been suppressed by growing Ge dots on silicon islands on the silicon oxide layer. A narrow peak of luminescence has been observed at 1550 nm. This phenomenon can be related to the narrowing of the size distribution of Ge dots on the Si islands. In the last part of this work, silicon nanowhiskers have been grown by molecular beam epitaxy on Si (111) by vapor-liquid-solid mechanism induced by gold droplets. Very thin Ge containing layers have been incorporated in Si nanowhiskers in order to grow SiGe heterostructures. Anomalous grazing incidence x-ray diffraction and transmission electron microscopy observations show a strong intermixing of Si with Ge in nanowhiskers and formation of SiGe heterostructures which are highly strained to Si.

MBE, quantum dots, nanostructures, nanowire, TEM, EJM, Ge, Si, RHEED, diffraction, EXAFS

On-line thesis.