Theory of near-interface trap quenching by impurities in SiC-based metal-oxide-semiconductor devices

Oxidizing SiC in the presence of various impurities (e.g., sodium, potassium, nitrogen, and phosphorous) has been previously observed to result in a significant reduction of the electron traps in the gate oxide near the SiC-SiO₂ interface. Here, we explore the electro-chemistry of the impurity elements involved using first-principles quantum mechanical calculations. Our results indicate that the observed reduction in the near interface traps (NITs) is not due to direct chemical passivation. Instead, we show that the quenching occurs because the NIT energy levels are lowered by the Coulombic tail of the positively charged impurities and thus become inaccessible to the experimental measurements. This new proposal explains a variety of experiments and leads to specific predictions.