The mechanism of defect creation and passivation at the SiC/SiO2 interface

From the viewpoint of application in power electronics, SiC possesses the greatest advantage of having SiO2 as its native oxide. Unfortunately, the usual thermal oxidation produces an unacceptably high density of interface states, with a complex energy distribution. Deep states are assumed to be caused by carbon excess at the interface, while the slow electron traps, called NIT, with especially high density near the conduction band of 4H- SiC ( which would be the best polytype for power devices), are expected to originate from oxide defects near the interface. Unlike the case of the Si/ SiO2 interface, simple hydrogen passivation does not help to reduce the high trap density. A possible passivation method for both deep states and NIT is post- oxidation annealing or oxidation in the presence of NO or N2O molecules. Here we present systematic and sophisticated theoretical calculations on a model of the 4H- SiC/ SiO2 interface, in order to establish the main reaction routes and the most important defects that are created during dry oxidation, and may give rise to the observed interface traps. We also investigate the effect of nitrogen in suppressing them.