SYNERGISM BETWEEN CHLORIDE AND PHOTONS IN THE INP DISSOLUTION MECHANISM

The chemical compositions of the surface oxides formed on InP, after etching in nitric or hydrochloric acid, were analyzed, mostly by x-ray diffraction (XRD). To facilitate analysis of the electrochemical behavior of InP in aqueous solutions, a potential-pH diagram for InP was established. Comparisons between results predicted from the potential-pH diagram and experimental results from XRD and inductively coupled plasma emission spectrometry (ICP) data showed good agreement. InPO4 was found to be the most thermodynamically stable solid phase, its region of stability covering much of the potential-pH diagram. This phase is also kinetically favored. The formation of InI and InI-InIII mixed valence chloro compounds and the great enhancement of the dissolution rate when InP is illuminated in the presence of Cl− evidently shows the ability of Cl− to participate in the dissolution of In and in the formation of InIII via an InI chloro intermediate. Measurements of InP dissolution rates under dark conditions in HC1 and inspection of the XRD pattern for the solid reaction product demonstrated the synergistic effect of Cl− and light on the dissolution process. A possible mechanism of nucleophilic attack of InP by Cl− under illumination is discussed in detail. © 1990, The Electrochemical Society, Inc. All rights reserved.