Impact of oxide/4H-SiC interface state density on field-effect mobility of counter-doped n-channel 4H-SiC MOSFETs

Abstract

We investigated the effect of interface state density on the field-effect mobility (μ FE) of 4H-SiC counter-doped metal-oxide-semiconductor field-effect transistors (MOSFETs). We fabricated counter-doped MOSFETs with three types of gate oxides i.e. SiO2, Al2O3 formed via atomic layer deposition, and Al2O3 formed via metal layer oxidation (MLO). A maximum μ FE of 80 cm2 V−1 s−1 was obtained for the MLO-Al2O3 FET, which was 60% larger than that of the SiO2 FET. In addition, we evaluated the electron mobility in the neutral channel (μ neutral) and the rate of increase in the free electron density in the neutral channel with respect to the gate voltage (dN neutral/dV G), which are factors determining μ FE. μ neutral depended only on the channel depth, independent of the type of gate oxide. In addition, dN neutral/dV G was significantly low in the SiO2 FET because of carrier trapping at the high density of interface states, whereas this effect was smaller in the Al2O3 FETs.