PHOTOELECTROCHEMICAL DISSOCIATION OF WATER AT SILICON DOPED N-GAAS ELECTRODES

The photoelectrochemical properties of silicon-doped n-GaAs were studied in aqueous solution of different pH values. The photosensitivity is higher in alkaline than in acidic solutions. However, visual photocorrosion, and deterioration of photocurrent could be observed after few hours of illumination in 0.1 M NaOH solution. The corrosion was decreased by coating the GaAs electrode with a 50 angstrom thick gold layer. If GaAs was used as an anode in an electrochemical cell. and illuminated with visible light (4200 angstrom < lambda < 6000 angstrom), photocurrent was observed due to the generation of H-2 over a Pt counter electrode. The photocurrent generated in 0.1 M NaOH solution has an onset potential of -1.1 V (NHE). Furthermore. it saturated at a potential of -0.3 V (NHE). Both the rate of H-2-production and photocurrent varied linearly with light intensity. The quantum efficiency for the hydrogen production is 0.4 hydrogen atom per second per photogenerated electron-hole pair. Our results are explained in the light of the band model of the semiconductor-solution interface.