Anomalous carbon clusters in 4H-SiC/SiO2 interfaces

We investigated a metal-oxide-semiconductor interface of dry-oxidized (000$\overline{1}$ ) 4H-SiC, which was known as the most electrically deteriorated SiC MOSFET, by electrically detected magnetic resonance (EDMR) and observed a signal with an isotropic g factor (2.0024) and magnetic-field angular dependent signal widths. Judging from the g factor, the signal comes from sp²-bonded carbon clusters. In addition, we found that the angular dependence of EDMR signal widths was caused by two-dimensional dipolar broadening with exchange interaction between electron spins. However, the density of electron spins or carbon clusters was 5.4 × 10¹³ cm⁻², which was not high enough for exchange interaction. Therefore, we propose inhomogeneous distribution of carbon clusters in the interface. At the interface, π* peaks from sp²-bonded carbon atoms were detected by electron energy loss spectroscopy. Scanning the electron beams along the interface revealed uneven existence of the π* peaks, which also proved that the sp²-bonded carbon atoms were distributed inhomogeneously in the interface. In addition, we found the formation of sp²-bonded carbon clusters at 4H-SiC(000$\overline{1}$ )/SiO₂ interfaces and interaction between π-conjugate electron spins on the carbon clusters by first principles calculation. Such carbon clusters generated electrically active states widely in the energy gap of 4H-SiC. The states result in the Fermi level pinning of the MOSFET.