Effect of quantum confinement on the defect-induced localized levels in 4H-SiC(0001)/SiO2 systems

In the present study, we characterize the nature of interface states in silicon carbide (SiC) metal–oxide–semiconductor (MOS) systems by analyzing the electrical characteristics of MOS field effect transistors (MOSFETs) based on the results of numerical calculations. In the calculation, the potential distributions and energy sub-bands were calculated by solving Poisson and Schrödinger equations, respectively. As a result, we demonstrate that the defect-induced localized levels in the bandgap are subjected to quantum confinement at the inversion layer, leading to the increase in their energy levels. The result implies that the conventional interface defects (e.g., near-interface oxide traps), which create defect states at certain energy levels measured from the vacuum level, are unlikely to be the major origin of the interface states in SiC MOS systems. The interface state density is almost uniquely determined by the oxide formation process (as oxidation or interface nitridation) and independent of the acceptor concentration (3 × 1015–1 × 1018 cm−3). It is also suggested that the drain current decrease observed in heavily doped MOSFETs is mainly due to the decrease in the drift mobility rather than that in the free carrier density.