Evidence of Channel Mobility Anisotropy on 4H-SiC MOSFETs with Low Interface Trap Density

In this work, we have evaluated 4° off-axis Si face 4H-SiC MOSFETs channel performance along both the [11-20] (perpendicular to steps) and [1-100] (parallel to steps) orientations, to evidence possible anisotropy on Si-face due to roughness scattering effect. Improved gate oxide treatments, allowing low interface state densities and therefore high mobility values, have been used on both NO and N2O annealed gate oxides. With these high channel mobility samples, a small anisotropy effect (up to 10%) can be observed at high electric fields. The anisotropy can be seen both at room and high temperatures. However, the optical phonon scattering is the dominant effect under these biasing conditions.