Quantitative Comparison of Fermi Level Pinning at GaAs / Metal and GaAs / Liquid Junctions

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Abstract
Flatband potential of (100)‐oriented electrodes in various aqueous solutions have been determined by ac impedance measurements. The Nernstian variation of with pH (−60 mV/pH) was verified in both indifferent electrolytes and redox‐couple solutions. Taking into account this pH dependence, the barrier height of the junction with various redox couples could be calculated. was determined at the point of zero zeta potential (PZZP), where the voltage drop due to specific adsorption of OH groups vanishes. A pH (PZZP) of 2.8 was estimated from published data for the electron affinity of . The variation of as a function of redox potential at the junction could then be quantified through the slope of the straight line. A value of was found, showing that Fermi level pinning is much weaker than at the junction, at which one has . The behavior is confirmed by published data on and polymer‐coated . We discuss these results within the framework of recent works on the semiconductor/metal Schottky barrier.

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