Electroreflection semiconductor-electrolyte interface

The theoretical developments in the above areas were influenced, to a considerable extent, by concepts borrowed from semiconductor physics and the physics of surfaces. Other fields of photoelectrochemistry of semiconductors were affected to a greater degree by progress achieved in the study of metal electrodes. Here we mean photoemission of electrons from semiconductors into solutions and electroreflection at a semiconductor-electrolyte interface. 

Photoelectrochemistry (PEC) is emerging from the research laboratories with the promise of significant practical applications. One application of PEC systems is the conversion and storage of solar energy. Chapter 4 reviews the main principles of the theory of PEC processes at semiconductor electrodes and discusses the most important experimental results of interactions at an illuminated semiconductor-electrolyte interface. In addition to the fundamentals of electrochemistry and photoexcitation of semiconductors, the phenomena of photocorrosion and photoetching are discussed. Other PEC phenomena treated are photoelectron emission, electrogenerated luminescence, and electroreflection. Relationships among the various PEC effects are established. 

Abrantes L. M., Peat R., Peter L. M. and Hamnett A. (1987), Electroreflectance at the semiconductor-electrolyte interface—a comparison of theory and experiment for n-GaAs , Ber. Bunsenges. Phys. Chem. 91, 369-374. 

Tafalla D., Pujadas M. and Salvador P. (1989), Direct measurements of flat-band potential shifts under illumination of the semiconductor electrolyte interface by electrolyte electroreflectance , Surface Sci. 215, 190-200. 

The detailed interpretation of electroreflectance spectra is still in its infancy, but enough has already been learnt to indicate that the technique will form a most valuable adjunct to other methods that have recently been developed to study the semiconductor/electrolyte interface. The next few years should see this technique become a standard weapon in the armoury of the semiconductor electrochemist. 

The reflectivity of a solid/electrolyte interface is often found to change with electrode potential, even in the absence of any faradaic reaction. This change in reflectance with potential, BR/dU, is commonly called electroreflectance (ER). In contrast to semiconductor where the externally applied... 

Electrolyte Electroreflectance (EER) is a sensitive optical technique in which an applied electric field at the surface of a semiconductor modulates the reflectivity, and the detected signals are analyzed using a lock-in amplifier. EER is a powerful method for studying the optical properties of semiconductors, and considerable experimental detail is available in the literature. ( H, J 2, H, 14 JL5) The EER spectrum is automatically normalized with respect to field-independent optical properties of surface films (for example, sulfides), electrolytes, and other experimental particulars. Significantly, the EER spectrum may contain features which are sensitive to both the AC and the DC applied electric fields, and can be used to monitor in situ the potential distribution at the liquid junction interface. (14, 15, 16, 17, 18)... 

Gilman J. M. A., Batchelor R. A. and Hamnett A. (1993), Surface processes at electrolyte highly-doped semiconductor interfaces analysed by electroreflectance modelling , J. Chem. Soc. Earaday Trans. 89, 1717-1722. 

Electroreflectance. The system s response here is the surface reflectivity. The technique is based on modulating the reflectivity of the semiconductor with low frequency bias voltage across the device. If the junction Is being formed with an electrolyte, the technique becomes known as Electrolyte Electroreflectance (EER). Excellent review articles cover the applications of this technique for analysis of optical properties of semiconductors and in the determination of the potential distribution across the interface of a solid or a liquid junction (59). 

---