Accurate evaluation of interface state density in SiC metal-oxide-semiconductor structures using surface potential based on depletion capacitance

We propose a method to accurately determine the surface potential (ψS) based on depletion capacitance, and the interface state density (DIT) was evaluated based on the difference between quasi-static and theoretical capacitances in SiC metal-oxide-semiconductor capacitors (C−ψS method). We determined that this method gives accurate values for ψS and DIT. From the frequency dependence of the capacitance measured at up to 100 MHz, a significant fast-interface-state response exists at 1 MHz, which results in the overestimation of ψS if it is determined based on the flatband capacitance at 1 MHz. The overestimation of ψS directly affects the accuracy of the energy level. DIT at a specific energy level is underestimated by the overestimation of ψS. Furthermore, the fast interface states that respond at 1 MHz cannot be detected by the conventional high(1 MHz)-low method. The C−ψS method can accurately determine the interface state density including the fast states without high-frequency measurements.