Photocorrosion inhibition -of n -GaAs in acidified aqueous iodide solution

Abstract

The photocorrosion of n-GaAs electrodes in aqueous solutions represents one of the most important factors limiting their application in solar energy conversion. In continuation of previous studies, the corrosion of n-GaAs has been investigated in 0·5M H₂SO₄ using a pllOtoelectrochemical cell. Illumination of the n-GaAs anode with white light of intensity 20 mW cm^-2 generated a saturation photocurrent of 27 mA cm^-2 at biasing voltages more positive than +0·45 V(SCE). This current corresponded to hydrogen discharge at the platinum counter electrode and to oxidation of the GaAs surface. When 0·01-6·0M LiI was added to the H₂SO₄ solution, 12 was formed at the n-GaAs electrode and dissolved in the iodide solution. The onset potential of the photocurrent (E_p) shifted from -0·36 to -0·73 V(SCE) as the concentration was varied from 0·01 to 6·0M I^-. Addition of I^- ₃ shifted E_p to more positive values. The extent of corrosion was studied by comparing the ratios of photogenerated I₂ and H₂. In 0·01, 1·0, and 6·0M I^- solutions, I₂/H₂ was 0·38, 0·87, and ∼1 respectively. These ratios imply that, at lower I^- concentrations, the holes photogenerated at the n-GaAs surface were consumed in the simultaneous oxidation of I^- and GaAs. However, in 6·0M I^-, where I₂/H₂ = 1, surface oxidation of GaAs was completely suppressed owing to total consumption of the photogenerated holes by the oxidation of I^-. The results are considered on the basis of the band model of the semiconductor/electrolyte interface.