Anomalous band alignment change of SiO2/4H-SiC (0001) and (000-1) MOS capacitors induced by NO-POA and its possible origin

For SiO2/4H-SiC (0001) and (000-1) n-type metal-oxide-semiconductor capacitors, the relationship between flatband voltage and the thickness of oxide was investigated after NO post-oxidation annealing to evaluate the expected flatband voltage (V-FB) without a fixed charge effect. After removal of the fixed charge effect, there was an anomalous negative shift of V-FB on (0001) 4H-SiC, which would be attributed to the result of dipole layer formation at the interface. The effects of the dipoles were investigated from the perspective of the SiO2/4H-SiC band alignment shift. We could find the correlation between the shift of V-FB and that of the band alignment between SiO2 and the 4H-SiC interface; we concluded that stable Si-N bonds at the interface induce a dipole layer, and this is one of the reasons for the unexpected shift reported for V-FB or threshold voltage of metal-oxide-semiconductor field-effect transistors, as well as the fixed charge effects. A significant difference in the band alignment on (0001) and (000-1) was also clarified, which would be one of the reasons for the disagreement of V-FB on those faces.