Anodic Dissolution of III-V Compound Semiconductors

In order to simplify this discussion. Fig. 1 schematically represents the main features of the current density / vs. potential K behavior of n- and p-type III-V electrodes in indifferent electrolyte solutions at (a) low and (b) high pH, in the dark and under illumination (Av E ). This generalized representation is primarily based on experimental results reported for GaAs and GaP for InP, less detailed data are available. Examples of actual experimental i- V curves are found in this text, as well as in the papers cited. 

It is interesting to consider in some detail the exponential region I in the p-type case. An important remark is that this region is situated negatively with respect to flat-band potential I fb. which implies that holes are being captured from a depletion layer. Assuming that the holes are at quasi-equilibrium in this layer, their con- 

Assuming further that the anodic current density is proportional to p, i. e., that the following relation holds  

The multi-equivalent anodic oxidation of the semiconductor involves several consecutive electrochemical steps, the first of which can be symbolized as 

The /- F behavior demonstrates that holes are involved in the anodic dissolution reactions the question arises, however, whether charge transfer occurs exclusively over the valence band. A straightforward way to investigate this problem is by comparing the number of photons absorbed in an n-type photoanode to the number of electrons flowing through the external circuit. This procedure has been used by Kohl et al. [33], and its results indicate a non-negligible contribution of the conduction 

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