Free electron concentration and carrier mobility measurements on 4H–SiC metal-oxide-semiconductor inversion layers are reported in this article. The key finding is that in state-of-the-art nitrided gate oxides, loss of carriers by trapping no longer plays a significant role in the current degradation under heavy inversion conditions. Rather, it is the low carrier mobility (maximum∼60 cm2 V−1 s−1) that limits the channel current. The measured free carrier concentration is modeled using the charge-sheet model and the mobility is modeled by existing mobility models. Possible mobility mechanisms have been discussed based on the modeling results.
For the first time, high power 4H-SiC n-IGBTs have been demonstrated with 13 kV
blocking and a low Rdiff,on of 22 mWcm2 which surpasses the 4H-SiC material limit for unipolar
devices. Normally-off operation and >10 kV blocking is maintained up to 200oC base plate
temperature. The on-state resistance has a slight positive temperature coefficient which makes the
n-IGBT attractive for parallel configurations. MOS characterization reveals a low net positive fixed
charge density in the oxide and a low interface trap density near the conduction band which produces
a 3 V threshold and a peak channel mobility of 18 cm2/Vs in the lateral MOSFET test structure.
Finally, encouraging device yields of 64% in the on-state and 27% in the blocking indicate that the
4H-SiC n-IGBT may eventually become a viable power device technology.
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