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Author

Mark Dynna

Date of Award

1993

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Materials Science and Engineering

Supervisor

G.C. Weatherly

Abstract

The energies of one and two-dimensional dislocation arrays lying near
a free surface are evaluated directly from the stress fields of single dislocations
in a half-space. These results are used to obtain expressions giving the
equilibrium spacings of a number of different arrays relieving misfit in a
strained epitaxial system. Numerical calculations are performed for the case of
edge and 60º dislocations relieving strain in a silicon-germanium layer
deposited on a silicon substrate. This method is also used to calculate the
energies of various low angle grain boundaries in a half-space.

Single-ended dislocation sources are observed using transmission
electron microscopy in two short-period Si-Ge superlattices grown on Si(100).
Their formation is linked to the development of non-planar layers during the
growth of the superlattices. The relaxation of these superlattices takes place
at significantly lower temperatures than equivalently strained homogeneous
epilayers.

Si-Ge short period superlattices deposited on Si(100) are shown to
relax through twinning on {111} planes if the deposited layers become grossly
non-planar. Twinning is accompanied by the formation of a diamond
hexagonal phase. No 60· a/2(110) dislocations relieving misfit are present in the strained layer structure.

The nature and origin of a new type of defect in Si₁_ᵪGeᵪ/Si strained
layer structures, the "pagoda" defect, is studied using transmission electron
microscopy. The defects are found to propagate in a direction determined by
the position of the Si source in unrotated substrates, and to have their origin
in the role played by SiC particles (left after cleaning the substrate) during
the growth process. Pits that form at the SiC particles are preserved during
MBE growth and perturb the strained layers, leading to the formation of
pagodas.