CHEMICAL MODIFICATION OF N-GAAS PHOTOANODES WITH GROUP-VIIIB METAL-IONS - STABILITY IN CONTACT WITH 1.0 M KOH(AQ)-0.10 M K2SE(AQ) SOLUTIONS AND IV PROPERTIES IN CONTACT WITH 1.0 M KOH(AQ)-0.3 M K2TE(AQ) ELECTROLYTES

A quantitative study has been performed on the stability of GaAs surfaces to photoanodic corrosion in contact with the 1.0 M KOH(aq)-0.10 M K2Se(aq)-0.01 M K2Se2(aq) electrolyte. In this electrolyte, chemically etched n-type GaAs electrodes displayed significant photocorrosion in competition with faradaic charge transfer to Se2-(aq). Chemisorption of group VIIIB metal ions, including complexes of Co(III), Os(III), and Ru(III), onto the etched GaAs surface yielded improved current-voltage (I-V) behavior of the GaAs photoanode and also resulted in a significant reduction in photocorrosion. This behavior implies that the chemisorbed metal ions act to increase the rate of hole transfer to the Se2- donor species, as opposed to the passivation of nonradiative surface recombination. Related experiments on n-GaAs photoanodes in contact with the 1.0 M KOH(aq)-0.3 M Te2-(aq)-0.01 M Te2(2-)(aq) electrolyte have also been performed. The I-V properties of n-GaAs, p-GaAs, and Sn-doped In2O3 electrodes have been investigated in this electrolyte, and these measurements have been used to elucidate common mechanistic features of charge-transfer reactions for the Se2-(aq) and Te2-(aq) redox systems.