starting epi growth

[lectures/latex.git] / posic / thesis / sic.tex

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@@ -142,12 +142,21 @@ This refined versions of the physical vapor transport (PVT) technique enabled th
 
 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 ...
-
-These defects include growth spirals (stepped screw dislocations), subgrain boundaries as well as micropipes (micron sized voids extending along the c axis of the crystal) in the hexagonal polytypes.
+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.
+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.
+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.
 
 \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, which will be exclusively reviewed in the following.
+
+
+
 \section{Ion beam synthesis of cubic silicon carbide}
 
 \section{Substoichiometric concentrations of carbon in crystalline silicon}