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 is a motivation with respect to the materials system, SiC.
+which in this case focuses on the materials system, SiC.
slide 2
-the semiconductor material SiC ...
+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+(nowadays superceded by direct band gap materials like GaN).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 3c 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 foolowed by a high-temperature annealing step
+turned out to constitute a promising method to form buried layers of SiC in Si.
+...
+
slide 5
+
+...
+
+and the task of this work is to gain insight into SiC precipitation in silicon.
+
slide 6
+
+this (insight) is achieved by atomistic simulations, which are explained after the assumed precipitation mechnisms present in literature are presented ...
+
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