To clarify the cause of the low channel conductivity at the SiO2/4H–SiC interface, the wavefunction at the SiC conduction band minimum was calculated using density functional theory under an applied electric field. We found that the wavefunction for a 4H–SiC (0001) slab tends to be localized at the cubic site closest to the interface. Importantly, because the conduction electrons are distributed closer to the interface (<5 Å) than expected from the effective mass approximation (EMA), they are more frequently scattered by interface defects. This is expected to be the reason why the channel conductivity for the (0001) face is particularly low compared with that for other faces, such as (11 2 ¯0). The breakdown of the EMA for the (0001) interface is related to the long structural periodicity along the [0001] direction in 4H–SiC crystals.

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