finisched cvd on sic

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

diff --git a/posic/thesis/sic.tex b/posic/thesis/sic.tex
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--- a/posic/thesis/sic.tex
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@@ -176,14 +176,18 @@ In summary, the almost universal use of Si has allowed significant progress in t
 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 statisfactory.
 
 The alternative attempt to grow SiC on SiC substrates has shown to drastically reduce the concentration of defects in deposited layers.
-By CVD, both, the 3C \cite{kong88,powell90,powell91} as well as the 6H \cite{kong88_2,powell90_2} polytype could be successfully grown.
+By CVD, both, the 3C \cite{kong88,powell90} as well as the 6H \cite{kong88_2,powell90_2} polytype could be successfully grown.
 In order to obtain the homoepitactically grown 6H polytype, off-axis 6H-SiC wafers are required as a substrate \cite{kimoto93}.
 %In the so called step-controlled epitaxy, lateral growth proceeds from atomic steps without the necessity of preceding nucleation events.
-Investigations indicate that in so-called step-controlled epitaxy, crystal growth proceeds through the adsorbtion of Si species at atomic steps and their carbonization by hydrocarbon molecules.
-A model is suggested ...
-
-... diffusion of reactants in a stagnant layer.
-
+Investigations indicate that in the so-called step-controlled epitaxy, crystal growth proceeds through the adsorbtion of Si species at atomic steps and their carbonization by hydrocarbon molecules.
+This growth mechanism does not require two-dimensional nucleation.
+Instead, crystal growth is governed by mass transport, i.e. the diffusion of reactants in a stagnant layer.
+In contrast, layers of the 3C polytype are formed on exactly oriented \hkl(0 0 0 1) 6H-SiC substrates by two-dimensional nucleation on terraces.
+However, lateral 3C-SiC growth was also observed on low tilt angle off-axis substrates originating from intentionally induced dislocations \cite{powell91}.
+Additionally, 6H-SiC was observed on clean substrates even for a tilt angle as low as \unit[0.1]{$^{\circ}$} due to low surface mobilities that facilitate arriving molecules to reach surface steps.
+Thus, 3C nucleation is assumed as a result of migrating Si and C cointaining molecules interacting with surface disturbances by a yet unknown mechanism, in contrast to a model \cite{ueda90}, in which the competing 6H versus 3C growth depends on the density of surface steps.
+
+MBE ... advantages ... and so on ...
 
 \section{Ion beam synthesis of cubic silicon carbide}