Calculation of the electrical impedance associated with the surface recombination of free carriers at an illuminated semiconductor/electrolyte interface

The impedance associated with recombination of free electrons and photoholes in surface states has been calculated. Two types of surface states have been considered: the so-called 'ordinary' surface states that are already present in the dark, and the surface states associated with intermediates of the photo-anodic decomposition. In both cases the result for the parallel equivalent surface state capacitance was characterised by a peak as a function of the electrode potential.