Structure, bonding, and passivation of single carbon-related oxide hole traps near 4H-SiC/SiO2 interfaces

摘要

Single carbon interstitial in silicon dioxide, existing in carboxyl configuration, is shown to act as a border hole trap near 4H-SiC/SiO interface. Using density functional theory-based formation energy considerations, it is found to switch charge state between +2 and neutral as the 4H-SiC Fermi level sweeps its charge transition level located 1.4 eV above 4H-SiC valence band edge. Thus, carboxyl defect is predicted to be a potential candidate for threshold voltage instability in 4H-SiC MOSFETs. Post oxidation annealing of the interface with nitric oxide is shown to remove carboxyl defects. However, treating the defect in H creates a hole trap level at 1.1 eV above 4H-SiC valence band edge similar to the original carboxyl defect. The stability of carboxyl and H treated carboxyl defects in their doubly positive state is explained on the basis of their structural and bonding transformations during hole capture. These include puckering and back-bonding of silicon with lattice oxygen as in the well-known oxygen vacancy (E′ center) hole traps and an increase in the bond order between carboxyl carbon and oxygen.