The dissolution and recombination processes at the CdS/electrolyte interface have been studied with the electrical and opto-electrical impedance methods. It has been found that dissolution intermediates can act as recombination centers and that thermal excitation of electrons from these intermediates to the conduction band can occur. In the case of the opto-electrical impedance it is shown that the modulation of the light intensity results in a modulation, not only of the minority carrier concentration, but also of the majority carrier concentration. As a consequence, a value for the Helmholtz capacitance could be determined from the opto-electrical impedance results.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 138.251.14.35 Downloaded on 2015-03-10 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 138.251.14.35 Downloaded on 2015-03-10 to IP

The electrical impedance and the optoelectrical impedance due to electron-hole recombination in the depletion layer and at the surface of a semiconductor electrode are calculated. It is shown that both types of impedance follow from a common formula for the ac recombination current density in the external circuit, which is derived from first principles. It is found that both the electrical and optoelectrical impedance methods provide the same information about recombination. Both methods enable one to distinguish surface recombination from recombination in the depletion layer. The theoretical results are compared with the electrical and optoelectrical impedance results measured at GaAs and CdS photoanodes.

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Dissolution of CdS in aqueous solutions of Br2 and I2 has been studied by ring‐disc voltammetry and flow‐cell measurements. The semiconductor is etched chemically at a considerable rate by Br2. CdS is dissolved in I2 solutions only when a high concentration of chloride ions is present. It is suggested that inter‐halogen species play a role. A novel chemical etching reaction was observed in the iodine case: cathodic reduction of iodine produces an intermediate capable of oxidizing the semiconductor.