Although significant advances have been achieved in the field of SiC bulk crystal growth, a variety of problems remain.
The high temperatures required in PVT growth processes limit the range of materials used in the hot zones of the reactors, for which mainly graphite is used.
-The porous material constitutes a severe source of contamination, e.g. with the dopants N, B and Al, which is exceptionally effective at low temperatures due to the low growth rate.
+The porous material constitutes a severe source of contamination, e.g. with the dopants N, B and Al, which is particularly effective at low temperatures due to the low growth rate.
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 mojor difficulty.
\subsection{SiC epitaxial thin film growth}
+Crystalline SiC layers have been grown by a large number of techniques on the surfaces of different substrates.
+Most of the crystal growth processes are based on chemical vapor deposition (CVD), solid-source molecular beam epitaxy (MBE) and gas-source MBE on Si as well as SiC substrates.
+In CVD as well as gas-source MBE, C and Si atoms are supplied by C containing gases like CH$_4$, C$_3$H$_8$, C$_2$H$_2$ or C$_2$H$_4$ and Si containing gases like SiH$_4$, Si$_2$H$_6$, SiH$_2$Cl$_2$, SiHCl$_3$ or SiCl$_4$ respectively.
+In the case of solid-source MBE atoms are provided by electron beam evaporation of graphite and solid Si or thermal evaporation of fullerenes.
+The following review will exclusively focus on CVD and MBE techniques.
+
+The availability and reproducibility of Si substrates of controlled purity made it the first choice for SiC epitaxy.
+The heteroepitaxial growth of SiC on Si substrates has been stimulated for a long time due to the lack of suitable large substrates that could be adopted for homoepitaxial growth.
+Furthermore, heteroepitaxy on Si substrates enables the fabrication of the advantageous 3C polytype, which constitutes a metastable phase and, thus, can be grown as a bulk crystal only with small sizes of a few mm.
+The main difficulties in SiC heteroepitaxy on Si is due to the lattice mismatch of Si and SiC and the difference in the thermal expansion coefficient of \unit[8]{\%}.
+Thus, in most of the applied CVD and MBE processes, the SiC layer formation process is split into two steps, the surface carbonization and the growth step, as proposed by Nishino~et~al. \cite{nishino83}.
+Cleaning of the substrate surface with HCl is required prior to carbonization.
+During carbonization the Si surface is chemically converted into a SiC film with a thickness of a few nm by exposing it to a flux of C atoms and concurrent heating up to temperatures about \unit[1400]{$^{\circ}$C}.
+In a next step, the epitaxial deposition of SiC is realized by an additional supply of Si atoms at similar temperatures.
+Low defect densities in the buffer layer are a prerequisite for obtaining good quality SiC layers during growth, although defect densities decrease with increasing distance of the SiC/Si interface \cite{shibahara86}.
+Next to surface morphology defects such as pits and islands, the main defects in 3C-SiC heteroepitaxial layers are twins, stacking faults (SF) and antiphase boundaries (APB) \cite{shibahara86,pirouz87}.
+
+
+off-axis \cite{shibahara86,powell87_2} ...
+resulting in carb and growth \cite{kitabatake97} ...
+
+lower temps ... to limit thermal stress due to differing expansion coefficients ...
+
\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 bulk silicon}
+\section{Assumed cubic silicon carbide conversion mechanisms}
\label{section:assumed_prec}
+on surface ... md contraction along 110 ... kitabatake ... and ref in lindner ... rheed from si to sic ...
+
+in ibs ... lindner and skorupa ...
+
+nejim however ...
+
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