AVS 49th International Symposium
    Surface Science Thursday Sessions
       Session SS+EL-ThA

Invited Paper SS+EL-ThA1
Epitaxial Growth Dynamics of Semiconductor Quantum Dot Structures

Thursday, November 7, 2002, 2:00 pm, Room C-112C

Session: Growth & Etching on Semiconductor Surfaces
Presenter: S.R. Leone, University of California and Lawrence Berkeley National Laboratory
Correspondent: Click to Email
The formation of Ge nanodots on Si(100) occurs by strain-induced mechanisms (Ge is 4% larger than Si) and obeys the Stranski-Krastanov (SK) growth mode: a wetting layer (3-5 layers) is followed by the formation of three-dimensional (3D) Ge structures. Quantitative studies of Ge island size distributions and their shape transformations, including huts, pyramids, domes, and superdomes, and shape changes due to annealing of the islands under the influence of surfactants, such as arsenic, are studied by molecular beam epitaxial growth and atomic force microscopy (AFM) post-analysis. For device applications, it is important to attain control over the size and spatial distributions of self-assembled nanostructures. The Ge growth experiments are also carried out on patterned silicon substrates (mesas formed by electron beam lithography followed by etching), for specific positioning of the dots. A 'one island on one mesa' relationship is achieved. The density of islands is higher than can normally be produced on unpatterned silicon, where island coalescence would usually occur well before this density is possible. Preferential growth on the tops of the mesas most likely occurs because the Si mesa tops are deformable, fulfilling a strain relaxation condition. In this work, pyramid-type islands as small as 25 nm are also aligned on the mesa tops, and no limit to the size reduction of the islands is apparent, being controlled mainly by the size of the etched features that can be introduced.