Photoelectrochemical behavior of n-gallium arsenide electrodes in ambient-temperature molten-salt electrolytes

Abstract

Photoelectrochemical (PEC) characterization of n-GaAs electrodes was carried out in room-temperature molten-salt electrolytes by using the aluminum chloride-butylpyridinium chloride (AlCl/sub 3/-BPC) system as a representative example. The working potential limits for the above electrodes in the melts, containing varying ratios of AlCl/sub 3/ and BPC, were established by cyclic voltammetry. Flat-band potential (V/sub fb/) measurements on n-GaAs in the same melts enabled location of the semiconductor band edge positions relative to the melt stability windows. In electrolytes containing AlCl/sub 3/ and BPC in the 1:1 molar ratio, the available range of potential was wide enough to probe the entire band-gap region. On the other hand, the potentials corresponding to the conduction band edges of n-GaAs were beyond the cathodic stability limit of both the 2:1 and 0.75:1 AlCl/sub 3/-BPC compositions. The electrode dissolution behavior of illuminated n-GaAs electrodes was investigated by cyclic voltammetry in melts of varying composition containing no intentionally added electroactive species. The onset of photoanodic corrosion currents was significantly positive of the values observed in aqueous electrolytes. The redox behavior of ferrocene-ferricenium ion couple (Fe(Cp)/sub 2//Fe(Cp)/sub 2//sup +/) was studied by cyclic voltammetry on vitreous carbon electrodes in the 2:1, 0.75:1, and 1:1 AlCl/sub 3/-BPC electrolytes. Underpotentialsmore » developed for the photoanodic process on n-GaAs relative to the reversible (dark) thermodynamic values on vitreous carbon were direct evidence for the sustained conversion of light energy to electrical energy.« less