High channel mobility in normally-off 4H-SiC buried channel MOSFETs

We have fabricated buried channel (BC) MOSFETs with a thermally grown gate oxide in 4H-SiC. The gate oxide was prepared by dry oxidation with wet reoxidation. The BC region was formed by nitrogen ion implantation at room temperature followed by annealing at 1500/spl deg/C. The optimum doping depth of the BC region has been investigated. For a nitrogen concentration of 1×10/sup 17/ cm/sup -3/, the optimum depth was found to be 0.2 μm. Under this condition, a channel mobility of 140 cm2/Vs was achieved with a threshold voltage of 0.3 V. This channel mobility is the highest reported so far for a normally-off 4H-SiC MOSFET with a thermally grown gate oxide.