Electrolyte-insulator-semiconductor surface states

By contrast, electrolyte states are much more limited in their distribution than metal conduction band states so that in many cases electron transfer through surface states may be the dominant process in semiconductor-electrolyte junctions. On the other hand, in contrast to vacuum and insulators, liquid electrolytes allow substantial interaction at the interface. Ionic currents flow, adsorption and desorption take place, solvent molecules fluctuate around ions and reactants and products diffuse to and from the surface. The reactions and kinetics of these processes must be considered in analyzing the behavior of surface states at the semiconductor-electrolyte junction. Thus, at the semiconductor-electrolyte junction, surface states can interact strongly with the electrolyte but from the point of view of the semiconductor the reaction of surface states with the semiconductor carriers should still be describable by equations 1 and 2. 

As discussed above only surface charging is of real importance for the interpretation of charge transfer at the semiconductor/electrolyte interface. The formation of a conducting layer leads to a solid state device, for which there is no need to be placed directly into the electrolyte. An insulating layer, on the other hand, can not improve charge transfer, except perhaps for very thin layers that allow electron tunneling. The band position at oxidized parts of the surface is not known. 

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