now starting ssmbe

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

diff --git a/posic/thesis/sic.tex b/posic/thesis/sic.tex
index 7fbc1a1..9ba0f13 100644 (file)
--- a/posic/thesis/sic.tex
+++ b/posic/thesis/sic.tex
@@ -116,6 +116,7 @@ Though possible, melt growth processes \cite{nelson69} are complicated due to th
 High process temperatures are necessary and the evaporation of Si must be suppressed by a high-pressure inert atmosphere.
 Crystals grown by this method are not adequate for practical applications with respect to their size as well as quality and purity.
 The presented methods, thus, focus on vapor transport growth processes such as chemical vapor deposition (CVD) or molecular beam epitaxy (MBE) and the sublimation technique.
+Excellent reviews of SiC formation have been published by Wesch \cite{wesch96} and Davis~et~al. \cite{davis91}.
 
 \subsection{SiC bulk crystal growth}
 
@@ -203,10 +204,10 @@ To realize single monolayer growth precise control of the gas supply to form the
 However, accurate layer-by-layer growth is achieved under certain conditions, which facilitate the spontaneous desorption of an additional layer of one atom species by supply of the other species \cite{hara93}.
 Homoepitaxial growth of the 6H polytype has been realized on off-oriented substrates utilizing simultaneous supply of the source gases \cite{tanaka94}.
 Depending on the gas flow ratio either 3C island formation or step flow growth of the 6H polytype occurs, which is explained by a model including aspects of enhanced surface mobilities of adatoms on a $(3\times 3)$ reconstructed surface.
-
-Problem of gas source ... strong adsorption and incorporation of atomic decomposited hydrogen of the gas phase reactants at low temperatures.
-Growth rate lower than desorption rate of hydrogen ...
-Solid source MBE may be the key to avoid such problems ...
+Due to the strong adsorption of atomic hydrogen \cite{allendorf91} decomposited of the gas phase reactants at low temperatures, however, there seems to be no benefit of GSMBE compared to CVD.
+Next to lattice imperfections, incorporated hydrogen effects the surface mobility of the adsorbed species \cite{eaglesham93} setting a minimum limit for the growth temperature, which would preferably be further decreased in order to obtain sharp doping profiles.
+Thus, growth rates must be adjusted to be lower than the desorption rate of hydrogen, which leads to very low deposition rates at low temperatures.
+Solid source MBE (SSMBE) may be the key to avoid these problems.
 Realized on and off-axis 3C on 4H and ... \cite{fissel95,fissel95_apl} ...
 Nonstoichiometric reconstruction plays a relevenat role ... handled by Si/C flux ratio ... \cite{fissel96,righi03} ...
 change in adlayer thickness and, consequently, in the surface super structure leading to growth of another polytype \cite{fissel95} ...