Light-modulated microwave conductivity

Light and potential modulated microwave reflectivity measurements offer a novel approach to the study of the semiconductor electrolyte interface. Perturbation of the density of electrons and holes in a semiconductor influences the conductivity and hence the imaginary component of the dielectric constant at microwave frequencies. For small perturbations, the change ARm in microwave reflectivity depends linearly on the change in conductivity [27, 28, 75). The application of frequency response analysis to light modulated microwave reflectance is relatively new [30]. Although the technique is analogous to IMPS, it provides additional information. 

The combination of photocurrent measurements with photoinduced microwave conductivity measurements yields, as we have seen [Eqs. (11), (12), and (13)], the interfacial rate constants for minority carrier reactions (kn sr) as well as the surface concentration of photoinduced minority carriers (Aps) (and a series of solid-state parameters of the electrode material). Since light intensity modulation spectroscopy measurements give information on kinetic constants of electrode processes, a combination of this technique with light intensity-modulated microwave measurements should lead to information on kinetic mechanisms, especially very fast ones, which would not be accessible with conventional electrochemical techniques owing to RC restraints. Also, more specific kinetic information may become accessible for example, a distinction between different recombination processes. Potential-modulation MC techniques may, in parallel with potential-modulation electrochemical impedance measurements, provide more detailed information relevant for the interpretation and measurement of interfacial capacitance (see later discus-... 

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