Extraction of interface state density at SiO2/SiC interfaces based on impedance measurements with different temperatures

We quantitatively compare density of interface states (Dit) at 4H-SiC/SiO2 interfaces evaluated by the high-low method, the Terman method and the conductance method. The results show that Dit evaluated from the Terman method exhibits the strong measurement temperature dependence and is lower than that evaluated from the other methods, indicating that it is difficult to accurately evaluate Dit in a wide range of surface potential by the Terman method. On the other hand, it is found that Dit by the conductance method is basically in agreement with Dit by the high-low method and is slightly higher near the conduction band edge. This result indicates that the conductance measurement allows us to detect interface states with shorter time constant and with surface potential closer to the band edge. Also, Dit by the conductance method has no measurement temperature dependence, confirming us the accuracy. These results suggest that the conductance method can detect more interface states than the Terman method and high-low method.