The energy distribution of electron states at SiC/SiO2 interfaces produced by oxidation of various (3C, 4H, 6H) SiC polytypes is studied by electrical analysis techniques and internal photoemission spectroscopy. A similar distribution of interface traps over the SiC bandgap is observed for different polytypes indicating a common nature of interfacial defects. Carbon clusters at the SiC/SiO2 interface and near‐interfacial defects in the SiO2 are proposed to be responsible for the dominant portion of interface traps, while contributions caused by dopant‐related defects and dangling bonds at the SiC surface are not observed.

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The electronic structure of SiC/SiO2 interfaces was studied for different SiC polytypes (3C, 4H, 6H, 15R) using internal photoemission of electrons from the semiconductor into the oxide. The top of the SiC valence band is located 6 eV below the oxide conduction band edge in all the investigated polytypes, while the conduction band offset at the interface depends on the band gap of the particular SiC polytype. In the energy range up to 1.5 eV above the top of the SiC valence band, interface states were found. Their electron spectrum is similar to that of sp2-bonded carbon clusters in diamond-like a-C:H films suggesting the presence of elemental carbon at the SiC/SiO2 interfaces.

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Low-temperature electrical measurements and photon-stimulated electron tunneling experiments reveal the presence of a high density of interface states at around 0.1 eV below the conduction band of 4H–SiC at its interface with thermally grown SiO2. These states, related to defects in the near-interfacial oxide layer, trap a considerable density of electrons from the SiC, and are likely responsible for the severe degradation of the electron mobility observed in the surface channel of 4H–SiC/SiO2 devices. The negative impact of the observed defects can be minimized by using SiC modifications (e.g., 6H, 15R, 3C) with a larger conduction band offset with the oxide than 4H–SiC leading to a largely reduced density of electrons trapped in the oxide.