Studies of polycrystalline n-GaAs junctions: effects of metal ion chemisorption on the photoelectrochemical properties of n-GaAs/KOH-Se-/2-, n-GaAs/CH3CN-ferrocene+/0, and n-GaAs/Au interfaces

Current-voltage and spectral response properties were determined for polycrystalline n-GaAs photoanodes in contact with aqueous KOH-Se^-/2- and nonaqueous CH₃CN-ferrocene^+/0-LiClO₄ electrolytes. The n-GaAs/KOH-Se^-/2- system initially exhibited poor junction behavior, but chemisorption of Ru^III, Rh^III, Ir^III, Co^III, or Os^III ions onto the GaAs photoanode was found to yield improved I-V properties. The trend in I-V improvement correlated with improved electrocatalysis of Se^2- oxidation at p-GaAs, n⁺-GaAs, and In₂O₃ electrode surfaces. The n-GaAs/CH₃CN system displayed excellent junction behavior and did not respond to metal chemisorption treatments. These results are consistent with the metal-ion-induced improvement being predominantly due to electrocatalytic effects.