On the electrochemical impedance of InP and GaAs electrodes in indifferent electrolyte. Part 1. Analytical description of the frequency dispersion

Abstract

Simple electrostatic theory describes a blocking semiconductor∣electrolyte contact as a perfect capacitor. This idealized behaviour of the interface does not correspond to the experimental fact that the capacitance of a semiconductor∣electrolyte contact very often depends on the measuring frequency (so-called ‘frequency dispersion’). The nature of this discrepancy remains largely unknown. In this paper, we show for n-InP and n-GaAs that the imperfect capacitor which a semiconductor∣electrolyte contact constitutes may be described as a parallel connection of a perfect capacitor, corresponding to the semiconductor space-charge layer, and a constant-phase element, describing the frequency dependence of the capacitance of the semiconductor∣electrolyte contact. Based upon the proposed equivalent circuit, the various interpretations of the frequency dispersion found in the literature are discussed. It is concluded that surface states may play a major role in the dispersion phenomenon.