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

Abstract

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 (VFB) without a fixed charge effect. After removal of the fixed charge effect, there was an anomalous negative shift of VFB 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 VFB 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 VFB 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 VFB on those faces.