Silicon carbide (SiC) is a promising material for applications in high-power and high-temperature electronic devices. Besides these highly desirable properties, SiC is the only compound semiconductor that can be thermally oxidized to form SiO2. However, SiC exhibits worse electrical passivation characteristics compared to Si due to the presence of silicon oxycarbide species that produce interfacial states at the oxide/SiC interface. For this reason, studies of the oxidation mechanism and chemical composition of thermally grown oxides on SiC have attracted a lot of attention recently.
The oxidation of Si-enriched SiC surfaces present interesting fundamental problems in terms of the sites where oxygen will favor an attack, and the possibility of forming well-ordered silicon oxide nanoclusters. Using first principals calculations, we studied the problem of oxygen insertion into well-ordered 3x3 reconstructed Si-enriched SiC nanoclusters.
The various configurations of physisorbed and chemisorbed oxygen have been identified and relaxed theoretically using the Gaussian98 suite. Transition states of the all the oxidation products have been ascertained and the activation energy for each oxygen-addition step has been calculated. The knowledge of activation energy for each oxygen-addition step allows quantitative and qualitative assessment of the most stable oxidation states. With this knowledge, we mapped out the potential energy diagram for the oxidation mechanism of Si-enriched SiC. This information, coupled with scanning tunneling microscopy (STM) images of the oxidation process, allowed us to identify the most stable oxidative products of the 3x3 reconstructed Si-enriched SiC surface.