Frequency and voltage dependency of interface states and series resistance in Al/SiO2/p-Si MOS structure

The capacitance-voltage (C-V) and conductance-voltage (G/ omega -V) characteristics of Al/SiO2/p-Si metal-oxide-semiconductor (MOS) Schottky diodes have been measured in the voltage range from -3 to +3 V and frequency range from 5 KHz to 1 MHz at room temperature. It is found that both C and G/ omega of the MOS capacitor are very sensitive to frequency. The fairly large frequency dispersion of C-V and G/ omega -V characteristics can be interpreted in terms of the particular distribution of interface states at SiO2/Si interface and the effect of series resistance. At relatively low frequencies, the interface states can follow an alternating current (AC) signal that contributes to excess capacitance and conductance. This leads to an anomalous peak of C-V curve in the depletion and accumulation regions. In addition, a peak at approximately -0.2 V appears in the Rs-V profiles at low frequency. The peak values of the capacitance and conductance decrease with increasing frequency. The density distribution profile of interface state density (Nss) obtained from CHF-CLF capacitance measurement also shows a peak in the depletion region.