Photoelectrochemistry of semiconductors

The separation of the conduction and valence bands provides a way to excite photons from the valence band to the conduction band. This is also the origin of a variety of photoelec-trochemical effects. Special monographs and reviews have been published, e.g., the book by Pleskov and Gurevich.  

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Kohei Uosaki received his B.Eng. and M.Eng. degrees from Osaka University and his Ph.D. in Physical Chemistry from flinders University of South Australia. He vas a Research Chemist at Mitsubishi Petrochemical Co. Ltd. from 1971 to 1978 and a Research Officer at Inorganic Chemistry Laboratory, Oxford University, U.K. bet veen 1978 and 1980 before joining Hokkaido University in 1980 as Assistant Professor in the Department of Chemistry. He vas promoted to Associate Professor in 1981 and Professor in 1990. He is also a Principal Investigator of International Center for Materials Nanoarchitectonics (MANA) Satellite, National Institute for Materials Science (NIMS) since 2008. His scientific interests include photoelectrochemistry of semiconductor electrodes, surface electrochemistry of single crystalline metal electrodes, electrocatalysis, modification of solid surfaces by molecular layers, and non-linear optical spectroscopy at interfaces. 

The photoelectrochemistry of semiconductors studies processes of various nature that occur at a semiconductor-electrolyte solution interface under the action of electromagnetic radiation (mainly in the visible, UV and IR regions). These processes include ... 

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. 

Finally, processes inverse to light-stimulated electrode reactions can also be referred to as processes of photoelectrochemistry of semiconductors. Such processes include, in particular, electrode reactions accompanied with light emission. 

Thus, photoelectrochemistry of semiconductors covers a fairly wide range of problems, which still continues to develop. 

Eventually, photoelectrochemistry of semiconductors emerged as an autonomous field of electrochemical physics after the works of Dewald (1960) who developed a detailed mechanism for the occurrence of photopotential at a semiconductor electrode. For greater details in the development of this early stage of photoelectrochemistry of semiconductors, the reader is referred, in particular, to the book by Myamlin and Pleskov (1967). 

This concluding part deals with a number of trends in photoelectrochemistry of semiconductors that have not so far been widely developed, the reasons often being of momentary character. At the same time, these trends are not only of significant scientific interest, but some of them may, in prospect, form the basis for important practical applications. In this respect, it appears to be quite reasonable to discuss the existing problems and the most important results. 

At present there is a sufficiently complete picture of photoelectrochemical behavior of the most important semiconductor materials. This is not, however, the only merit of photoelectrochemistry of semiconductors. First, photoelectrochemistry of semiconductors has stimulated the study of photoprocesses on materials, which are not conventional for electrochemistry, namely on insulators (Mehl and Hale, 1967 Gerischer and Willig, 1976). The basic concepts and mathematical formalism of electrochemistry and photoelectrochemistry of semiconductors have successfully been used in this study. Second, photoelectrochemistry of semiconductors has provided possibilities, unique in certain cases, of studying thermodynamic and kinetic characteristics of photoexcited particles in the solution and electrode, and also processes of electron transfer with these particles involved. (Note that the processes of quenching of photoexcited reactants often prevent from the performing of such investigations on metal electrodes.) The study of photo-electrochemical processes under the excitation of the electron-hole ensemble of a semiconductor permits the direct experimental verification of the applicability of the Fermi quasilevel concept to the description of electron transitions at an interface. 

Finally, a promising trend in the study of the photoelectrochemical behavior of objects, whose nature is close to that of semiconductors, is related to photobiology, in particular to processes of light conversion in natural photosynthesizing objects. Certain elementary stages of photosynthesis, particularly photoelectrochemical ones, can, apparently, be simulated in some cases within the framework of the concepts of photoelectrochemistry of semiconductors. 

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