Electro‐optical Investigation of the Potential Drop at III/V Semiconductor/Electrolyte Interfaces

The semiconductor/electrolyte junction is investigated for n‐type , , and in contact with aqueous and nonaqueous electrolytes. Electrolyte electroreflectance is used as an in situ probe for determining the distribution of potential and energy states at the interface. We find that interface states at and electrodes have a density of and , respectively, and that this density is pH independent for (semiconductor controlled), whereas for it is pH dependent (solvent controlled). For , the situation is more complex, and interfaces clean from energy states (density lower than 10¹² cm⁻² eV⁻¹) can be obtained at pH 0 as well as a complete Fermi level pinning (density ∼10¹⁵ cm⁻² eV⁻¹) depending on the bias. At ^pH 14 and in propylene carbonate, the interface states density is large and bias independent. Therefore, we conclude that two types of interface states may exist, electrochemical (pH 0) and chemical (pH 14), and the former cannot be removed electrochemically.