Temperature dependence of Fowler-Nordheim current in 6H- and 4H-SiC MOS capacitors

This work reports on Fowler-Nordheim (F-N) injection studies on n-type 6H-SiC and 4H-SiC MOS systems under positive gate bias from 25 to 325/spl deg/C. At a given temperature and electric field, the current density in the 4H-SiC MOS system is about five times higher than that in 6H-SiC due to the smaller effective barrier height for the 4H-SiC MOS system as compared to 6H-SiC. The reduction of the effective barrier height with temperature, particularly in 4H-SiC, raises serious concerns about the long-term reliability of gate oxides in SiC. It is concluded that the maximum practical values of electric field in the 4H-SiC MOS system under positive gate bias and high junction temperature should be reduced to below the values used in the Si MOS system.