Analysis of fast and slow responses in AC conductance curves for p-type SiC MOS capacitors

We used a conductance method to investigate the interface characteristics of a SiO2/p-type 4H-SiC MOS structure fabricated by dry oxidation. It was found that the measured equivalent parallel conductance–frequency (Gp/ω–f) curves were not symmetric, showing that there existed both high- and low-frequency signals. We attributed high-frequency responses to fast interface states and low-frequency responses to near-interface oxide traps. To analyze the fast interface states, Nicollian's standard conductance method was applied in the high-frequency range. By extracting the high-frequency responses from the measured Gp/ω–f curves, the characteristics of the low-frequency responses were reproduced by Cooper's model, which considers the effect of near-interface traps on the Gp/ω–f curves. The corresponding density distribution of slow traps as a function of energy level was estimated.