Electron Excitation Studies of Anodic Dissolution Mechanisms

3 Electron Excitation Studies of Anodic Dissolution Mechanisms 

In the above section, various dissolution mechanisms for III-V compound electrodes were proposed on the basis of stabilization studies. There is evidently a need for confirmation of these mechanisms from independent data. Such confirmation can be obtained by quantitatively studying the enhancement of the anodic dark current at n-type electrodes, caused by hole injection. Although, as mentioned in Sec. 2.1, this effect has been known for many years, only recently was it realized [41] that the relationship between the additional anodic current density 4 and the cathodic hole injection current density constitutes a powerful probe for in- 

As /a was found to increase with temperature [40,41], step (51) is believed to be an activated process, in which the electron must first be thermally excited from the Xj surface state to the conduction band edge before injection can occur. The corresponding current density is therefore usually referred to as the electron excitation current density. The reaction step with which reaction (51) is assumed to compete is then step (15) in the DH dissolution mechanism, step (37) in the DX mechanism, step (46) (or (46 )) in the DXC mechanism, and equally step (46) or (46 ) in the DHC mechanism, which we have hitherto not considered, and which comprises the following steps  

The coefficients Q through C9 are positive pH-independent combinations of rate constants. 

The described and similar reaction schemes have been worked out according to the usual steady-state treatment in order to obtain the corresponding 4 vs. relationships. The results of these calculations, for which we refer to the literature [40, 41, 64], are summarized in Table 1. It should be noted that for both mechanisms. 

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