Light modulated microwave reflectivity interfaces

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. 

For the very small perturbations involved in the measurements, the light modulated microwave reflectivity change, ARm is a linear function of the ac component of the photogenerated charge that accumulates at the sem-iconductor/electrolyte interface... 

Schlichthorl et al. [177] have used light modulated microwave reflectivity to derive the rates of interfacial electron transfer processes at the n-Si/electrolyte interface. In these measurements, the modulation frequency was constant, and the rate constants for charge transfer were derived from the potential dependent ARm response. Schlichthorl et al. [73] have extended the technique considerably by introducing frequency response analysis. The technique is therefore analogous to IMPS, although, as shown below, it provides additional information. 

If krec = 0, the photocurrent simply follows the illumination step and contains no information about the rate of charge transfer at the interface. The comparison shows that, unlike IMPS and PEIS, light modulated microwave reflectivity measurements still provide kinetic information at high band bending where recombination is negligible and the steady state photocurrent is described by the Gartner equation. 

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