Simulations of the Steady-State Current Density vs Potential Characteristics of Semiconducting Electrodes

Abstract

A series of digital simulations has been performed to obtain insight into the steady-state current density vs potential behavior of semiconductor/liquid interfaces. The ToSCA program, incorporating all of the key kinetic parameters involved with the generation, transport, and recombination of charge carriers both in the semiconductor and across the semiconductor/liquid interface, has been used for this purpose. The simulations confirmed conclusions obtained previously from a simplified analytical model, which state that for ideal behavior of a nondegenerately doped semiconducting electrode the photovoltage of an n-type semiconductor/liquid interface should not change if the concentration of the reduced form of the redox species, A⁻, is held constant but the concentration of the oxidized form of the redox species, A, is varied. The simplified analytical model also predicts that the photovoltage will be independent of variation in [A⁻] if [A] is held constant. In contrast, recent work has asserted that ideal junction behavior implies that the photocurrent should exhibit shifts in potential that are linearly dependent on the concentration of the minority carrier acceptor species in the solution, with a magnitude of 59 mV per decade change in the acceptor concentration at 300 K. In accord with the predictions of the simplified analytical model, such shifts are not apparent in the simulations presented in this work. Finally, ToSCA simulations have been applied to analyze literature data on the steady-state current density vs potential behavior of p-InP/Fe(CN)₆^(3-/4-)(aq) contacts. Such simulations have established an upper bound for the interfacial charge-transfer rate constant of kₑₜ ≈ 10⁻²⁰ cm⁴ s⁻¹ in this system.

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