AVS 49th International Symposium
    Nanometer Structures Tuesday Sessions
       Session NS+EL-TuA

Paper NS+EL-TuA6
Spontaneous Generation of Free-Standing Ge Quantum Dots on Silicon-on-Insulator

Tuesday, November 5, 2002, 3:40 pm, Room C-207

Session: Quantum Dots
Presenter: E.A. Sutter, Colorado School of Mines
Authors: E.A. Sutter, Colorado School of Mines
P.W. Sutter, Colorado School of Mines
P. Zahl, Colorado School of Mines
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The growth of heteroepitaxial materials on engineered composite substrates such as silicon-on-insulator (SOI) opens a new route for controlling the structural and electronic properties of materials at the nanoscale. Local lattice strain induced by Ge quantum dots grown coherently on SOI - a composite of an ultrathin monocrystalline Si template supported by amorphous SiO@sub 2@ on a conventional Si wafer, causes significant local distortion in the Si template and can be used as a tool for nanoscale band structure engineering of the Si substrate. The Ge islands themselves form on SOI initially as huts and then transform into domes, similar to the sequence of epitaxially constrained shapes they assume on bulk Si (100). While the shape sequence of epitaxial Ge islands on bulk Si ends here, we observe further dramatic morphological changes on ultrathin SOI: a spontaneous transformation to free-standing Ge islands accompanied by a breakup of the thin Si slab. We use a combination of atomic force microscopy (AFM) and transmission electron microscopy (TEM) to document the sequence of shape transformations of Ge islands on SOI. We investigate in detail the island shape evolution and redistribution of the substrate material between the islands both before and after the breakup of the ultrathin Si slab of the SOI substrate.