\chapter{Review of the silicon carbon compound}
\label{chapter:sic_rev}

\section{Structure, properties and applications of silicon carbide}

The phase diagram of the C/Si system is shown in Fig.~\ref{fig:sic:si-c_phase}.
In the solid state the stoichiometric composition of silicon and carbon termed silicon carbide (SiC) is the only chemical stable compound in the C/Si system \cite{scace59}.
\begin{figure}[ht]
\begin{center}
\includegraphics[width=12cm]{si-c_phase.eps}
\end{center}
\caption[Phase diagram of the C/Si system.]{Phase diagram of the C/Si system \cite{scace59}.}
\label{fig:sic:si-c_phase}
\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}.
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 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 covalent $\sigma$ bonds of equal length and strength for each atom with its neighbours.
Although the local order of Si and C next neighbour 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.
\begin{figure}[ht]
\begin{center}
\includegraphics[width=12cm]{polytypes.eps}
\end{center}
\caption{Stacking sequence of SiC bilayers of the most common polytypes of SiC (from left to right): 3C, 2H, 4H and 6H.}
\label{fig:sic:polytypes}
\end{figure}
Fig.~\ref{fig:sic:polytypes} shows the stacking sequence of the most common and technologically most important SiC polytypes, which are the cubic (3C) and hexagonal (2H, 4H and 6H) polytypes.

\begin{table}[ht]
\begin{center}
\begin{tabular}{l c c c c c c}
\hline
\hline
 & 3C-SiC & 4H-SiC & 6H-SiC & Si & GaN & Diamond\\
\hline
Hardness [Mohs] & \multicolumn{3}{c}{------ 9.6 ------}& 6.5 & - & 10 \\
Band gap [eV] & 2.36 & 3.23 & 3.03 & 1.12 & 3.39 & 5.5 \\
Break down field$^{\text{A}}$ [$10^6$ V/cm] & 4 & 3 & 3.2 & 0.6 & 5 & 10 \\
Saturation drift velocity$^{\text{A}}$ [$10^7$ cm/s] & 2.5 & 2.0 & 2.0 & 1 & 2.7 & 2.7 \\
Electron mobility$^{\text{B}}$ [cm$^2$/Vs] & 800 & 900 & 400 & 1100 & 900 & 2200 \\
Hole mobility$^{\text{B}}$ [cm$^2$/Vs] & 320 & 120 & 90 & 420 & 150 & 1600 \\
Thermal conductivity [W/cmK] & 5.0 & 4.9 & 4.9 & 1.5 & 1.3 & 22 \\
\hline
\hline
\end{tabular}
\end{center}
\caption[Properties of SiC polytypes and other semiconductor materials.]{Properties of SiC polytypes and other semiconductor materials. Doping concentrations are $10^{16}\text{ cm}^{-3}$ (A) and $10^{17}\text{ cm}^{-3}$ (B) respectively. References: \cite{wesch96,casady96,park98}. {\color{red}Todo: add more refs + check all values!}}
\label{table:sic:properties}
\end{table}
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.
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.
In addition the high thermal conductivity enables the implementation of small-sized electronic devices enduring increased power densites.
Despite high-temperature operations the wide band gap also allows the use of SiC in optoelectronic devices.
Indeed, a forgotten figure, Oleg V. Losev discovered what we know as the light emitting diode (LED) today in the mid 1920s by observing light emission from SiC crystal rectifier diodes used in radio receivers when a current was passed through them\cite{losev}.
Apparently not known to Losev, Henry J. Round published a small note\cite{round} reporting a bright glow from a SiC diode already in 1907.
However, it was Losev who continued his studies providing comprehensive knowledge on light emission of SiC (entitled luminous carborundum) and its relation to diode action\cite{losev,losev,losev,losev} constituting the birth of solid-state optoelectronics.
And indeed, the first significant blue LEDs reinvented at the start of the 1990s were based on SiC\cite{foobar}.
Due to the indirect band gap and, thus, low light emitting efficiency, however, it is nowadays replaced by GaN based diodes.
Focus on ... key ... to high efficiency

The wide band gap ... light emitting diodes ... first blue led ... but GaN direct band gap semiconductor ...
However ... combine all electr properties ... high-* .. .devices diodes, inverters ... 
break down field and high thermal conductivity ... high-densea and high-power ...
high saturation drift velocity high-frequency ...
Mechanical stability almost like diamond ...
Chemical inert, low neutron capture foobar ... radiation hardness

Since in this work 3C-SiC unit cell ... two fcc lattices ...


\section{Fabrication of silicon carbide}

SiC usually manmade.
The unique properties driving its applications in the same time harden the fabrication of SiC ...

\section{Ion beam synthesis of cubic silicon carbide}

\section{Substoichiometric concentrations of carbon in crystalline silicon}

\section{Assumed precipitation mechanism of cubic silicon carbide in silicon}
\label{section:assumed_prec}

