Ultrashallow defects in SiC MOS capacitors

Capacitance-voltage measurements performed at cryogenic temperatures (14 – 500 K) have been used to determine the ultrashallow interface states in SiC MOS capacitors. These states occupies energy levels in SiC band gap on different energy levels up to 27 meV below the conduction band. Moreover, the capacitance-voltage characteristics are moving to lower voltages with temperature increasing, indicating a reduction in flat band voltage from 14.65 (14 K) to 2.77 V (500 K). It was demonstrated that a complete ionization of the nitrogen donors from the epitaxial layer occurs at 420 K. From these analysis, an activation energy of around 26.79 meV was determined. In order to determine the energy levels distribution of the interface states in SiC band gap, the Fermi level variation with temperature was calculated, starting from a value of around 27.1 meV at 14 K and reaching a value of 321 meV at 500 K under SiC conduction band. Six peaks (D₁ – D₆) have been identified in interface states density distribution at different levels of energy in SiC band gap, which could correspond to different defects at the SiO₂/SiC interface.