On the frequency-dependence of the impedance of n- and p-type gallium arsenide electrodes

The impedance of n- and p-type GaAs electrodes has been studied as a function of applied voltage and of frequency. Simple frequency laws were found to exist for the series capacitance and resistance. To explain these laws, a distribution of time constants has been assumed, associated with dielectric relaxation phenomena in the double-layer at the semiconductor/electrolyte interface. This distribution was found to be independent of the distance from the crystal surface for n-type samples but to depend upon it for p-type specimens. An investigation on the role of the applied voltage in these frequency laws yielded additional evidence for the mathematical model which was originally introduced in a previous paper in order to explain similar laws observed at CdSe, CdS and TiO₂ electrodes. The frequency-dispersion of the p-type samples was found to be strongly influenced by an appropriate pretreatment of the surface, in contrast with the behaviour of the n-type specimens. In both cases, the experimental results indicate that the source of the frequency dispersion has to be sought in structural irregularities of the depletion region of the electrode. The possibility of determining the flat-band potential from frequency-dependent impedance data is discussed.