EXPERIMENTAL INVESTIGATION OF CHARGE-TRANSFER AT THE SEMICONDUCTOR ELECTROLYTE JUNCTION

The behavior of the semiconductor/electrolyte contact is dominated by the exchange of charges at the interface. In this respect, an understanding of the transfer kinetics is vital in the description of the phenomena and few methods are able to unambiguously characterize it. The problems related to this question are surveyed, paying particular attention to recently developed Tafel plot measurements. The method, based on the systematic determination of the band edge position as a function of the current flow, has been applied to some important aspects of the semiconductor/liquid junction such as corrosion, stabilization mechanisms and the effect of deposition of dispersed catalysts. Chronologically, the latter system is at the origin of this type of measurement, when it was realized that the exchange current deduced from Tafel plots was identical to that existing between the solution and the deposited catalyst. The generalization of this approach in subsequent studies shows that Tafel plots of semiconductor electrodes constitutes a simple and quantitative technique which can provide real access to transfer mechanisms. At the same time, our technique highlights the parallel between the electrochemistry at metal and semiconductor substrates. For the latter it is shown that the effect of the different potential drops (in the material, in the double layer) at the interface can be experimentally uncoupled.