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

We report an N2 based annealing treatment to passivate interface traps (Dit) 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 Dit 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. Dit 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 Dit 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 Dit and explains the difference in Dit characteristics with nitrogen areal density between n- and p-type interfaces.