Metal-inducd assembly of a semiconductor-island lattice: Getruncated pyramids on Au-patterned Si Page: 4 of 16
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studies of Ge growth on Au-free Si (001).19,20,21 The presence of a Ge wetting layer in the Au-patterned
region has been detected as well.
Gold was not detected in the islands within the atomic-percent-level sensitivity of EDS.
Nevertheless, the role of Au in producing the surprising difference in island shape cannot be discounted
as even a small amount of Au on the surface may modify surface energies and drive the observed
faceting. Thus far, we know that Sn can be used instead of Au to direct island organization; when Sn is
used, island shapes are markedly different from the TP shape observed on Au-patterned Si. Further
studies are under way.
Observations of island shape evolution at low coverages (1.5 ML-3 ML) reveal that TP islands
originate from lens-like islands at center sites. The largest lens-like islands develop distinct facets
marking the boundary with the substrate and evolve into TP islands that continue to grow with further
deposition as well as by coarsening presumably through the consumption of the smaller islands, which
disappear. Evolution of islands into the TP shape results in a dramatic change in island dimensions as
shown in Figure 3. At intermediate coverages (4 ML-8 ML), one to three almost fully evolved
truncated pyramidal islands are found at each center site. Above 8ML a one-TP-island-per-site
relationship is widely observed (Figure la). We note that coherent TP islands have been observed in the
growth of SiipxGex (for x up to 0.3) islands on Si (001) by liquid-phase epitaxy,22,23 in which similar
island growth dynamics appear to be at play. We therefore believe that the growth of SiGe islands by
Ge and Si co-evaporation onto a metal-patterned substrate is likely to result in coherent (dislocation-
free) island arrays.
Substrate orientation plays an important role in determining island shape. Beyond the TP shapes
observed on Si (001), islands grown on Au-patterned Si (111) have an approximately tetrahedral island
shape. Germanium growth on Au-patterned Si (110) results in two-fold symmetric, rod-shaped islands,
which are preceded at low Ge coverages by lens-like islands. These observed shapes-TP, tetrahedral,
and rod-like-are consistent with the symmetry of the growth surface.
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Robinson, J.T.; Liddle, J.A.; Minor, A.; Radmilovic, V.; Yi,D.O.; Greaney, P.A. et al. Metal-inducd assembly of a semiconductor-island lattice: Getruncated pyramids on Au-patterned Si, article, August 28, 2005; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc892927/m1/4/: accessed October 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.