Verlag des Forschungszentrums Jülich
JUEL-3599
The island size distribution after submonolayer deposition
of Si on Si(111)exhibits pronounced peaks of magic sizes. It
is possible to study directly the influence of surface
reconstruction on growth kinetics by in vivo STM. Lateral
growth of rows of the width of the 7 x 7 reconstruction unit
cell leads to kinetic stabilization of magic islands.
Kinetic Monte Carlo simulations are performed that reproduce
the main experimental results and make it possible to
estimate important energy barriers.
The influence of elastic stress was examined in Ge/Si
growth. The StranskiKrastanov wetting layer of Ge/Si(001)
exhibits a 2 x N reconstruction. For coverages from 0.8 ML
to 2 ML the value of N decreases from 16 to 8. The 2 x N
reconstruction below 1 ML and its evolution in time give
evidence for intermixing of Ge and Si.
Above 2 ML threedimensional Ge islands with {105} facets
known as hut clusters are observed. The evolution of size
and shape of individual hut clusters is followed by in vivo
STM. A slower growth rate is observed when an island grows
to larger sizes. This behaviour can be explained by
self-limiting growth. A kinetic growth model involving a
nucleation barrier for each repeated growth of a new atomic
layer on the {105} facets agrees with the experimental
results for the evolution of the island volume. The
experimentally observed transition from nearly square shaped
islands to elongated islands is described by the kinetic
growth model.
For Ge/Si(111) the decay of twodimensional islands is
monitored after the evaporation was terminated. Islands
which are two monolayers high decay faster than islands
which are one layer high. Thermodynamically stable
twodimensional islands are not observed. It is found that
the stable structures are threedimensional islands probably
relaxed by misfit dislocations.
When a molecular beam is directed from the side towards the
Si sample while the STM tip is stationary and close to the
sample surface, the tip shades part of the sample surface.
The edge of the shadow can be studied by STM imaging after
the evaporation. A sharp edge is found upon deposition of Si
or Ge, but a smooth edge is observed for Sb. Two facts might
explain this difference: first, the bonding of Sb to the Si
substrate is much stronger than the bonding beteween
successive layers of Sb, second, the Sb beam consists of
quadrumeres rather than single atoms. Kinetic Monte Carlo
simulations show that strong bonding to the substrate is
essential for a smooth transition, while possible diffusion
of quadrumeres with finite lifetime is not.
Kästner, Martin
Untersuchung dynamischer Prozesse bei der Molekularstrahlepitaxie auf Silizium
140 S., 1998
Dynamical processes in thin film growth using molecular beam
epitaxy (MBE) are studied with a recently developed
experimental technique called in vivo scanning tunneling
microscopy (in vivo STM). With this method, it is possible
to follow the evolution of specific features during growth.
Homoepitaxial growth on Si(111) and heteroepitxial growth of
Ge/Si(001) are investigated. In addition, the shadow of the
STM tip is used to study the edges of shaded areas in MBE.
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