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Heteroepitaxial growth of Ge on Si(001) is extremely important
for at least two reasons: first, it has great potential as a
substrate for new, high frequency semiconductor devices, while
remaining compatible with existing Group IV technology; and
second, it is a prototypical system for studying strained
Stranski-Krastanow growth.
We are studying this growth using electronic structure techniques.
A well-defined series of reconstructions results as increasing
amounts of Ge is deposited on the Si(001) surface, which increases
the strain. Our studies are broken down into several areas:
The (2xn) reconstruction for sub-monolayer
coverages. This work used ab initio density
functional calculations, and has been published in Surface Science
(vol. 515, p. 483). It is available as a preprint in either
gzipped postscript or PDF. An example of this system
is illustrated above for n=6.
Multilayer growth of Ge on Si(001): the (MxN)
reconstruction. This work used tight binding
calculations (using the DensEl
code), validated against the earlier ab initio
work. It has been accepted for publication in Surface Science, and is
available as a preprint in either gzipped postscript or PDF. An example of the results
is shown below in three different views: from above, from the
front (i.e. looking up the page in the first picture) and from
the side (i.e. looking across the page in the first
picture).
Top
Front
Side
The step roughness reversal seen with Ge on Si(001).
The Si(001) surface has two kinds of step (A-type, which is
parallel to the underlying dimer rows and B-type, which is
perpendicular to the dimer rows). The A-type steps are
generally very straight, while the B-type steps are often
kinked. When Ge is added, this roughness reverses, and
eventually steps form along the elastically soft (100) and
(010) directions, just prior to the formation of "hut"
clusters. We are investigating these processes with tight
binding.
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