The structural and electrical characterisation of SiGe heterostructures deposited on strain relaxed virtual substrates
Hammond, Richard (1998) The structural and electrical characterisation of SiGe heterostructures deposited on strain relaxed virtual substrates. PhD thesis, University of Warwick.
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The influence of lateral dimensions on the relaxation mechanism and the
resulting effect on the surface topography of limited-area, linearly graded
Si1-xGeX virtual substrates has been investigated for the first time.
A dramatic change in the relaxation mechanism of such buffer layers has
been observed for depositions on Si mesa pillars of lateral dimensions of 10μm
and below. For such depositions, misfit dislocations are able to extend,
unhindered, and terminate at the edges of the growth zone. In this manner,
orthogonal misfit dislocation interactions are avoided, yielding a surface free of
the problematic surface cross-hatch roughening.
However, as the lateral dimension of the growth zone is increased to
20μm, orthogonal misfit interactions occur and relaxation is dominated by the
Modified Frank-Read (MFR) multiplication mechanism. The resulting surface
morphology shows a pronounced surface cross-hatch roughening. It is
proposed that such cross-hatch roughening is a direct consequence of the
cooperative stress fields associated with the MFR mechanism.
It is postulated that the method of limited-area, linearly graded buffer
layers provides a unique opportunity, by which 'ideal' virtual substrates, free
of surface cross-hatch and threading dislocations, may be produced to any Ge
In addition, a unique method by which the electrical performance of low
temperature, strained layer depositions may be optimised is discussed. The
method relies on the elimination, 'of as-grown lattice imperfections via a post
growth thermal anneal treatment. A 25-fold increase in low temperature hole
mobility of a Si0.5Ge0.5/Si0.7Ge0.3 heterostructure has been demonstrated using a
30 minute, 750°C in-situ, post growth anneal.
|Item Type:||Thesis or Dissertation (PhD)|
|Subjects:||Q Science > QC Physics
T Technology > TK Electrical engineering. Electronics Nuclear engineering
|Library of Congress Subject Headings (LCSH):||Semiconductors -- Design and construction, Germanium, Silicon, Heterostructures|
|Official Date:||September 1998|
|Institution:||University of Warwick|
|Theses Department:||Department of Physics|
|Supervisor(s)/Advisor:||Parker, E. H. C. ; Whall, Terry E.|
|Extent:||xiv, 127 p.|
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