The electrochemical impedance of one-equivalent electrode processes at dark semiconductor/redox electrodes involving charge transfer through surface states. 2. The n-GaAs/Fe3+ system as an experimental example

In this paper, an electrochemical study of the n-GaAs/Fe3+ system is presen ted. Combining the results of current density vs potential, Mott-Schottky, and electrochemical impedance measurements, it is shown that charge transfe r through surface states is the most plausible reaction mechanism for the F e3+ to Fe2+ reduction at the n-GaAs electrode. On the basis of the experime ntal impedance spectra and of the theoretical equivalent circuit derived in part 1 (Hens, Z. J. Phys. Chem. 1998, 103, 122), the charge-transfer mecha nism is analyzed in detail. The Fe3+ reduction rate shows a marked evolutio n as a function of time which, basing upon the electrochemical impedance re sults, is attributed to an increase in the number of surface states.