A REAPPRAISAL OF THE FREQUENCY-DEPENDENCE OF THE IMPEDANCE OF SEMICONDUCTOR ELECTRODES

The frequency dependence of the impedance of polarizable semiconductor/metal and semiconductor/electrolyte solution interfaces is reconsidered. No frequency dispersion of the polarization capacitance is found with n-GaAs/Au contacts whereas the capacitance of n-GaAs/electrolyte solution interfaces show considerable dispersion. The frequency dispersion depends on the microroughness of the electrode surface and on the specific conductivity of the electrolyte solution. As for polarizable metal electrodes, the relationship between the capacitance and the frequency is closely related to the relationship between the capacitance and the specific conductivity of the electrolyte solution. It is concluded that the main origin of frequency dispersion should not be sought in the solid but is related to the development of the electric double layer at the electrolyte side of the interface. A model is presented to account for these results.