Trap passivation of 4H-SiC/SiO₂ interfaces by nitrogen annealing

We report an N₂ based annealing treatment to passivate interface traps (D_it) in n- and p-type 4H-SiC. The process has the potential to replace the commonly used hazardous and expensive gas nitric oxide (NO). N₂ postoxidation annealing reduces D_it in both the upper and lower halves of the 4H-SiC bandgap, with a greater impact at the valence band edge. N₂ annealing at 1500 °C is observed to be more effective in passivating traps and positive fixed charges than NO annealing for p-type devices, whereas for n-type devices, the opposite is true. The breakdown voltages for these devices are found to be lower than that of NO annealed devices. X-ray photoelectron spectroscopy has been performed to estimate the nitrogen areal density at the interface. D_it is measured as a function of nitrogen areal densities in the near interfacial regions for the different processes. Theoretical analysis through density functional theory is consistent with the measured D_it profiles by showing the generation of additional states near the valence band edge due to increased nitrogen concentration. In addition to reporting the effect of N₂ annealing on both n- and p-type 4H-SiC, this work correlates the nitrogen areal densities at the interface to the D_it and explains the difference in D_it characteristics with nitrogen areal density between n- and p-type interfaces.