On the electrochemical impedance of blocking semiconductor vertical bar electrolyte contacts

From electrostatic theory, it follows that a blocking semiconductor\electro lyte (sle) contact should constitute a perfect capacitor. However, the expe rimentally observed interfacial capacitance of an sie contact depends very often on the measuring frequency. In this paper, the relation between sie i nterfacial capacitance and applied frequency is established using the p-InP \0.1 M H2SO4 system as an example. The electrochemical impedance of this in terface may be simulated - apart from the series resistance of the cell - b y a parallel connection of a resistor, a capacitor and a constant-phase ele ment (CPE). Next, it is shown that the magnitude of the CPE coefficient - e ither in the case of p-InP, n-InP or n-GaAs in H2SO4-containing aqueous sol utions - is related to the conductivity of the electrolyte. No straightforw ard relation between the CPE and the surface morphology could be retrieved. A description of the sie interface that accounts for the experimental resu lts on the dispersion phenomenon at s\e interfaces is proposed. Localized l evels at the semiconductor surface are considered to be essential to the ob served frequency dependence of the interfacial capacitance. These surface s tates are related partially to crystal damage caused by the electrode produ ction process. Interaction between the surface states and the electrolyte m ay account for the relation between dispersion and electrolyte conductivity observed.