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

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. SiO 2 , Al 2 O 3 formed via atomic layer deposition, and Al 2 O 3 formed via metal layer oxidation (MLO). A maximum μ FE of 80 cm 2 V −1 s −1 was obtained for the MLO-Al 2 O 3 FET, which was 60% larger than that of the SiO 2 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 SiO 2 FET because of carrier trapping at the high density of interface states, whereas this effect was smaller in the Al 2 O 3 FETs.