Faradaic currents on semiconductors

Electron transfer at semiconductors can be contrasted with that at metal electrode surfaces. In the latter case, as shown in Fig. 41(a), electron transfer normally takes place to or from energy levels within a few kT of the Fermi 

A second distinction between metals and semiconductors is also found. For metals, the concentration of carriers is so high that the transport of these carriers to the surface is rarely, if ever, a limiting factor. The situation for semiconductors is quite different even the concentration of majority carriers may be sufficiently low for transport to constitute a severe limitation on the maximum current attainable and, if the current is primarily due to minority carriers, the generation and transport of these will almost always be rate limiting. 

One further distinction needs to be drawn, though this distinction also exists on a metal electrode surface faradaic processes may involve both weak and strong interactions. The former would be typified by outer-sphere transfer from electrode to solution redox couple and theoretical progress in understanding this type of process has been considerable in the last two decades. Strong interactions between the surface and the redox species include such processes as anodic or cathodic corrosion of a metal or semicon- 

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