Remarkable increase in the channel mobility of SiC-MOSFETs by controlling the interfacial Si[O.sub.2] layer between [Al.sub.2][O.sub.3] and SiC

N-channel planar [Al.sub.2][O.sub.3]/Si[O.sub.2]/SiC MOSFETs are fabricated and the effect of a Si[O.sub.2] layer inserted between [Al.sub.2][O.sub.3] and SiC is examined. The results have shown that the interface property of the ultrathin Si[O.sub.2]/SiC structure is very good, but the interface property has degraded when the Si[O.sub.2] thickness is larger than 2 nm due to interfacial layer formation.