-Depending on the gas flow ratio either island formation or step flow growth occurs, which is explained by a model including aspects of enhanced surface mobilities of adatoms on a reconstructed surface.
-{\color{red} Read, understand and mabye add a bit more.}
-
-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 ...
+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.
+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 constitute the preffered method to avoid these problems.