High-Mobility 4H-SiC p-Channel MOSFETs on Nonpolar Faces

The p-channel MOSFETs on 4H-SiC (1100) and (1120) with various donor concentrations of n-body (10 15 –10 17 cm -3 ) were fabricated. The gate oxide was formed by oxidation followed by NO annealing. The (1100) and (1120) MOSFETs exhibited about two-fold mobility on (0001). The highest mobility of 28 cm 2 /Vs ever reported for SiC p-channel MOSFETs was achieved on (1100). The interface state density near the valence band edge on (1100) and (1120) is lower than that on (0001). It was found that the channel mobility perpendicular to the c-axis is 20– 50% higher than that parallel to the c-axis. The anisotropy of channel mobility originates from the anisotropy of effective mass of holes in the inversion layer, which is based on the calculation of the effective mass taking account of three different holes (heavy hole, light hole, and crystal-field split-off hole) in 4H-SiC and quantum confinement effects in the inversion layer.