Using electrically-detected-magnetic-resonance spectroscopy and a device simulation, we studied dominant interface defects, named "C-face defects," in C-face 4H-SiC metal-oxide-semiconductor field-effect transistors (MOSFETs). The C-face defects act as hole traps via their donor levels, when they are not passivated by hydrogen atoms. The densities of unpassivated C-face defects were estimated to be from 4×10~(12) cm~(-2) to 13×10~(12) cm~(-2) in various C-face MOSFETs, which correlated with negative threshold-voltage (V_(th)) shifts. We explained influences of the C-face defects on the V_(th) instability and the channel mobility of C-face MOSFETs.
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