Small surface potential fluctuation near the valence band edge at nitrided 4H-SiC(0001)/SiO2 interfaces

Interface states near the valence band edge at a nitrided 4H-SiC(0001)/SiO2 interface were investigated by the conductance, C–ψS, and high-low methods. Consistent energy distribution of the interface state density was extracted by the conductance and C–ψS methods. The interface state density at EV+0.2 eV is 3.9×1012cm−2eV−1, which is comparable to that at EC−0.2 eV. The standard deviation of the surface potential fluctuation obtained by the conductance method is as small as 3–13 meV near the valence band edge, which is significantly smaller than that near the conduction band edge (∼100 meV). This finding indicates that the scattering caused by the surface potential fluctuation is much smaller in SiC p-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) than in n-channel MOSFETs, which would be one of the reasons for the relatively high mobility in SiC p-channel MOSFETs.