slide 1

dear examiners, dear colleagues.
welcome everybody to the the defense of my doctor's thesis entitled ...
as usual, i would like to start with a small motivation,
which in this case focuses on the materials system, SiC.
and, thereby, approach the problem to be investigated within this study.

slide 2

the semiconductor material SiC has remarkable physical and chemical properties,
which make it a promising new material in various fields of applications.
the wide band gap and high breakdown field
as well as the high electron mobility and saturation drift velocity
in conjunction with its unique thermal stability and conductivity
unveil SiC as the ideal candidate for
high-temperature, high-power and high-frequency electronic
and opto-electronic devices.

in fact light emission from SiC crystal rectifiers was observed
already in the very beginning of the 20th century
constituting the brirth of solid state optoelectronics.
and indeed, the first blue light emitting diodes in 1990 were based on SiC.
(nowadays superceded by direct band gap materials like GaN).

the focus of SiC based applications, however,
is in the area of solid state electronic devices
experiencing revolutionary performance improvements enabled by its capabilities.
devices can be designed much thinner with increased dopant concentrations
resulting in highly efficient rectifier diodes and switching transistors.
one example is displayed: a SiC based inverter with an efficiency of 98.5%
designed by the frauenhofer institute for solar energy systems.
therefore, SiC constitutes a promising candidate to become the key technology
towards an extensive development and use of regenerative energies and emobility.

moreover, due to the large bonding energy,
SiC is a hard and chemical inert material
suitable for applications under extreme conditions
and for microelectromechanical systems.
its radiation hardness allows the operation as a first wall reactor material
and as electronic devices in space.

slide 3

the stoichiometric composition of silicon and carbon
is the only stable compound in the C/Si system.
SiC is a mainly covalent material in which both,
the Si and C atom are sp3 hybridized.
the local order of the silicon and carbon atoms
characterized by the tetrahedral bond is the same for all polytypes.
however, more than 250 different polytypes exist,
which differ in the one-dimensional stacking sequence of
identical, close-packed SiC bilayers,
which can be situated on one of three possible positions (abbreviated a,b,c).
the stacking sequence of the most important polytypes is displayed here.
the 3c polytype is the only cubic polytype.

different polytypes exhibit different properties,
which are listed in the table
and compared to other technologically relevant semiconductor materials.
Despite the lower charge carrier mobilities for low electric fields,
SiC clearly outperforms Si.
among the different polytypes, the cubic phase shows the highest
break down field and saturation drift velocity.
additionally, these properties are isotropic.
thus, the cubic polytype is most effective for highly efficient
high-performance electronic devices.

slide 4

SiC is rarely found in nature and, thus, must be synthesized.
it was first observed by moissan from a meteor crater in arizona.
the fact that natural SiC is almost only observed
as individual presolar SiC stardust grains near craters of meteorite impacts
already indicates the complexity involved in the synthesis process.

however, nowadays, much progress has been achieved in SiC thin film growth.
indeed, commerically available semiconductor devices based on alpha SiC exist,
although these are still extremely expensive.
however, production of the advantageous cubic polytype material is less advanced.
mismatches in the thermal expansion coefficient and the lattice parameter
(with respect to the substrate) cause a considerable amount of defects,
which is responsible for structural and electrical qualities
that are not yet satisfactory.

next to CVD and MBE, the ion beam synthesis technique, which consists of
high dose ion implantation followed by a high-temperature annealing step
turned out to constitute a promising method to form buried layers of SiC in Si
as indicated in this sketch.
due to the high areal homogenity achieved in ibs
the size is only limited by the beam scanning equipment
and sythesized films do not exhibit surface bending effects
in contrast these formed by cvd and mbe.
this enables the synthesis of large are SiC films.

slide 5

the ibs synthesis of ...

and the task of this work is to gain insight into SiC precipitation in silicon.

slide 6

supposed conv mech


slide 7

however, controversial ... exists in literature

slide 8

this (insight) is achieved by atomistic simulations, which are explained after the assumed precipitation mechnisms present in literature are presented ...

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