Investigation of carbon contaminations in $SiO2$ films on $4H-SiC(0001)$

$SiO2$ films can be grown on SiC by oxidation of the clean SiC surfaces. During the oxidation process carbon atoms have to leave the crystal. This occurs by outdiffusion of CO molecules from the reaction front through the growing film. Carbon atoms remaining at the interface or in the oxide film lead to an increased density of states in the band gap, and therefore lower the quality of the $SiO2∕SiC$ interface. In this work photoemission spectroscopy and photoelectron diffraction were used to study the carbon contamination in ultrathin $SiO2$ films on $4H-SiC(0001)$⁠. The contaminations were produced during oxidation at high temperatures and low oxygen pressure. Due to their chemical shift carbon atoms from the contaminations and from the substrate can be distinguished in the C $1s$ photoemission spectrum. A combined photoelectron spectroscopy and photoelectron diffraction study shows that these carbon agglomerations are similar to carbon enrichments observed after heating of clean SiC surfaces and that they are either amorphous clusters or have no preferential orientation with respect to the SiC substrate.