\end{figure}
SiC was first discovered by Henri Moissan in 1893 when he observed brilliant sparkling crystals while examining rock samples from a meteor crater in Arizona.
He mistakenly identified these crystals as diamond.
-Although they might have been considered \glqq diamonds from space\grqq{} Moissan identified them as SiC in 1904~\cite{moissan04}.
+Although they might have been considered \glqq diamonds from space\grqq{}, Moissan identified them as SiC in 1904~\cite{moissan04}.
In mineralogy SiC is still referred to as moissanite in honor of its discoverer.
It is extremely rare and almost impossible to find in nature.
SiC is a mainly covalent material in which both, Si and C atoms are sp$^3$ hybridized.
Each of the four sp$^3$ hybridized orbitals of a Si atom overlaps with one of the four sp$^3$ hybridized orbitals of the four surrounding C atoms and vice versa.
-This results in fourfold coordinated mostly covalent $\sigma$ bonds of equal length and strength for each atom with its neighbors.
+This results in fourfold coordinated, mostly covalent $\sigma$ bonds of equal length and strength for each atom with its neighbors.
Although the local order of Si and C next neighbor atoms characterized by the tetrahedral bonding is the same, more than 250 different types of structures called polytypes of SiC exist~\cite{fischer90}.
The polytypes differ in the one-dimensional stacking sequence of identical, close-packed SiC bilayers.
Each SiC bilayer can be situated in one of three possible positions (abbreviated a, b or c) with respect to the lattice while maintaining the tetrahedral bonding scheme of the crystal.
% todo add more refs + check all values!
Different polytypes of SiC exhibit different properties.
Some of the key properties are listed in Table~\ref{table:sic:properties} and compared to other technologically relevant semiconductor materials.
-Despite the lower charge carrier mobilities for low electric fields SiC outperforms Si concerning all other properties.
+Despite the lower charge carrier mobilities for low electric fields, SiC outperforms Si concerning all other properties.
The wide band gap, large breakdown field and high saturation drift velocity make SiC an ideal candidate for high-temperature, high-power and high-frequency electronic devices exhibiting high efficiency~\cite{wesch96,morkoc94,casady96,capano97,pensl93,park98,edgar92}.
-In addition the high thermal conductivity enables the implementation of small-sized electronic devices enduring increased power densities.
+In addition, the high thermal conductivity enables the implementation of small-sized electronic devices enduring increased power densities.
Its formidable mechanical stability, heat resistance, radiation hardness and low neutron capture cross section allow operation in harsh and radiation-hard environments~\cite{capano97}.
In addition to high-temperature operations, the wide band gap also allows the use of SiC in optoelectronic devices.
Among the different polytypes of SiC, the cubic phase shows a high electron mobility and the highest break down field as well as saturation drift velocity~\cite{neudeck95,wesch96}.
In contrast to its hexagonal counterparts 3C-SiC exhibits isotropic mechanical and electronic properties.
Additionally the smaller band gap is expected to be favorable concerning the interface state density in MOSFET devices fabricated on 3C-SiC~\cite{pensl00}.
-Thus the cubic phase is most effective for highly efficient high-performance electronic devices.
+Thus, the cubic phase is most effective for highly efficient high-performance electronic devices.
\begin{figure}[t]
\begin{center}
\includegraphics[width=0.35\columnwidth]{sic_unit_cell.eps}
Since the vapor pressure of Si is much higher than that of C, a careful manipulation of the Si vapor content above the seed crystal is required.
Additionally, to preserve epitaxial growth conditions, graphitization of the seed crystal has to be avoided.
Avoiding defects constitutes a major difficulty.
-These defects include growth spirals (stepped screw dislocations), subgrain boundaries and twins as well as micropipes (micron sized voids extending along the c axis of the crystal) and 3C inclusions at the seed crystal in hexagonal growth systems.
+These defects include growth spirals (stepped screw dislocations), subgrain boundaries and twins as well as micropipes (micron sized voids extending along the
+%c axis of the crystal)
+core of screw dislocations)~\cite{frank51,heindl97}
+and 3C inclusions at the seed crystal in hexagonal growth systems.
Micropipe-free growth of 6H-SiC has been realized by a reduction of the temperature gradient in the sublimation furnace resulting in near-equilibrium growth conditions in order to avoid stresses, which is, however, accompanied by a reduction of the growth rate~\cite{schulze98}.
Further efforts have to be expended to find relations between the growth parameters, the kind of polytype and the occurrence and concentration of defects, which are of fundamental interest and might help to improve the purity of the bulk materials.
APB defects, which constitute the primary residual defects in thick layers, are formed near surface terraces that differ in a single-atom-height step resulting in domains of SiC separated by a boundary, which consists of either Si-Si or C-C bonds due to missing or disturbed sublattice information~\cite{desjardins96,kitabatake97}.
However, the number of such defects can be reduced by off-axis growth on a Si \hkl(0 0 1) substrate miscut towards \hkl[1 1 0] by \unit[2]{$^{\circ}$}-\unit[4]{$^{\circ}$}~\cite{shibahara86,powell87_2}.
This results in the thermodynamically favored growth of a single phase due to the uni-directional contraction of Si-C-Si bond chains perpendicular to the terrace steps edges during carbonization and the fast growth parallel to the terrace edges during growth under Si rich conditions~\cite{kitabatake97}.
+% more up2date paper
+A reduction of the SF in addition to the APB defects was recently achieved by growing 3C-SiC on undulant Si~\cite{nagasawa06}, i.e.\ a Si \hkl(0 0 1) substrate covered with continuous slopes oriented in the \hkl[1 1 0] and \hkl[-1 -1 0] directions.
+In this way, APB defects are eliminated by a mechanism similar to that in the off-axis growth process while, at the same time, SFs are aligned in the \hkl(1 1 1) or \hkl(-1 -1 1) planes and, thus, terminate as they connect with each other during the growth process.
+%
By MBE, lower process temperatures than these typically employed in CVD have been realized~\cite{hatayama95,henke95,fuyuki97,takaoka98}, which is essential for limiting thermal stresses and to avoid resulting substrate bending, a key issue in obtaining large area 3C-SiC surfaces.
In summary, the almost universal use of Si has allowed significant progress in the understanding of heteroepitaxial growth of SiC on Si.
However, mismatches in the thermal expansion coefficient and the lattice parameter cause a considerably high concentration of various defects, which is responsible for structural and electrical qualities that are not yet satisfactory.
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