A Fully Determined System

At the beginning of this chapter we presented evidence that a combination of (photo)electrochemistry with photoinduced microwave conductivity measurements promises more direct access to kinetic parameters involv- 

The photoinduced microwave conductivity signal, on the other hand, can be described by the following integral over the excess minority carriers, to be taken over both the diffusion and the space charge region  

This means that the PMC signal will, apart from the generation rate of minority carriers and a proportionality constant, be determined by the interfacial charge transfer rate constant kr and the interfacial charge recombination rate sr 

There is an additional simple relation between the surface concentration Aps of photogenerated minority carriers and the charge recombination and charge transfer rates sr and kr to be considered  

These three equations (11), (12), and (13) contain three unknown variables, ApJt kn and sr The rest are known quantities, provided the potential-dependent photocurrent (/ph) and the potential-dependent photoinduced microwave conductivity are measured simultaneously. The problem, which these equations describe, is therefore fully determined. This means that the interfacial rate constants kr and sr are accessible to combined photocurrent-photoinduced microwave conductivity measurements. The precondition, however is that an analytical function for the potential-dependent microwave conductivity (12) can be found. This is a challenge since the mathematical solution of the differential equations dominating charge carrier behavior in semiconductor interfaces is quite complex, but it could be obtained,9 17 as will be outlined below. In this way an important expectation with respect to microwave (photo)electro-chemistry, obtaining more insight into photoelectrochemical processes 

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