Interfacial Anodic Behaviors of n- and p-GaAs Semiconductors in Liquid Ammonia at 223 K

Abstract

Using cyclic voltammetry, for both p- and n-type GaAs, an anodic peak is observed just before an unlimited anodic current, in acidic, neutral, or basic media in liquid ammonia. This anodic peak is due to an adsorption/precipitation phenomenon. It led to the passivation of the SC surface regardless of pH. After passivation of the electrode, a reduction wave appeared in acidic medium as well in unbuffered neutral medium, but in this last case only for high scan rates. In basic medium, no reduction wave appeared. The initial electrochemical state of GaAs, corresponding to the presence of the anodic peak, is recovered by reduction of the adsorbed film in acidic media, in unbuffered neutral medium, or in buffered neutral medium. No recovery is observed in basic media. These last results show that this recovery occurred only when protons came from the medium (acidic medium) or protons came from the anodic reaction associated to the anodic peak, or if a proton donor was present. Quantitative analysis of gallium and arsenic elements released in solution showed clearly that a dissolution happened without limitation as soon as the unlimited anodic current was reached. Coulometric measurements point out that the efficiency of dissolution increased with current density in the anodic unlimited current, showing that ammonia oxidation and material oxidation were concomitant reactions. The anodic wave may be considered as the result of the precipitation of a nitrogenous-based complex (i.e., amide complex) which implies the superficial lattice contribution. The passivation film may be initiated by the formation of strongly adsorbed atoms of nitrogen, intermediaries arising from ammonia oxidation, which can behave as site poison at the interface during nitrogen evolution. © 2003 The Electrochemical Society. All rights reserved.