Photoeffects in semiconductors

The origin of the large photoeffects often seen in extrinsic semiconductors is illustrated in Fig. 59. A positive bias creates, as we have already depletion layer of thickness W. If the total bias is V volts and ve = Ve0/kT, we have 

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Gartner WW (1959) Depletion layer photoeffects in semiconductors. Phys Rev 116 84-87... 

Experimental observation of photoemission currents encounters the problem of separating them from the currents of photoelectrochemical reactions of nonemission nature, which are caused by the internal photoeffect in the semiconductor (see, for example, Section 5). Photoprocesses of both the types start similarly with the interband excitation of an electron and are of threshold character with respect to the frequency of light, but the threshold quantum energy is different for these processes. Namely, the threshold of photoemission exceeds that of the internal photoeffect (and hence the threshold of ordinary photoelectrochemical reactions) by the value of the electron affinity to the semiconductor % (see Figs. 31 and 32). 

This can partly explain the differences found for the two electrodes. The somewhat preliminary results shown here demonstrate that large effects of this kind can be found and one has to take into account the anisotropy of light absorption in the study of photoeffects at semiconductor electrodes. 

This volume, based on the symposium Photoeffects at Semiconductor-Electrolyte Interfaces, consists of 25 invited and contributed papers. Although the emphasis of the symposium was on the more basic aspects of research in photoelectrochemistry, the covered topics included applied research on photoelectrochemical cells. This is natural since it is clear that the driving force for the intense current interest and activity in photoelectrochemistry is the potential development of photoelectrochemical cells for solar energy conversion. These versatile cells can be designed either to produce electricity (electrochemical photovoltaic cells) or to produce fuels and chemicals (photoelectrosynthetic cells). 

Photoeffects on Semiconductor Ceramic Electrodes. Photoresponse of SrTiCh found to be better than that of BaTiCh. Unlike the use of single crystals in the above studies (Entries 1-3), polycrystalline electrodes with large area were used. 389... 

Semiconductor photoeffects in a complex redox electrolyte are greatly affected by such solution properties as solution redox level and stability, interfacial kinetics (adsorption), conductivity, viscosity, ionic activity, and transparency within a crucial wavelength region. Suitable redox electrolytes are known to inhibit unfavourable phenomena such as surface recombination and trapping (McEvoy et al, 1985). In... 

CaheuD., Hodes G., Manassen J. and Tenne R. (1980), Stability of cadmium chalcogenide-based photoelectrochemical cells , in Photoeffects at Semiconductor Electrolyte Interfaces, Nozik A. J. (ed.), ACS Symp. Ser. No. 146, 369-385. 

Mlyasaka, T. Honda, K In ACS Symposium Series Photoeffects at Semiconductor-Electrolyte Interfaces American Chemical Society Washington, D.C., 1980 p. 1. 

The discussion of photoeffects in terms of quasi-Fermi levels may seem to be rather pointless because there is no way of determing the quasi-Fermi levels at solid-solid junctions experimentally. It has been introduced here, however, because it is possible to obtain experimental information on quasi-Fermi levels in the case of semiconductor-liquid junctions, and it will be shown in Chapter 7 that the same principles can be applied for semiconductor-liquid and solid-solid junctions. 

McGregor, K.G., Calvin, M., Otvos, J.W. Photoeffects in Fc203 sintered semiconductors. 

As was true for that of photoeffects, the objective of this discussion of noise mechanisms is to acquaint the reader with the broad concepts of noise in detectors without deriving in great detail the appropriate equations. See Van Vliet [2.141] for a detailed treatment. Nevertheless, it will be necessary to present certain equations which describe the dependence of noise upon internal material parameters and external system parameters. The discussion will consider initially noise in semiconductor detectors, followed by noise in photoemissive devices. 

Josephson detector Photoeffect on Cooper pairs in semiconductor within a Josephson junction... 

It is only to be expected that some nonequilibrium detector stmctures have their analogs in semiconductor lasers. Exclusion detectors correspond to single-hetero-lasers, extraction devices to double-heterolasers, and magnetoconcentration detectors to lasers with the magnetoelectric photoeffect proposed by Marimoto et al. [331]. This inverse analogy is valid not only in electrical, but also in optical field, where e.g., resonant cavity (RCE) detector structures are connected with VCSEL lasers, and lasers with a PBG cavity with PCE (photonic crystal-enhanced) detectors. 

T. Morimoto, M. Chiba, G. Kido, A. Tanaka, Stimulated emission due to the magnetoelectric photoeffect in narrow-gap semiconductors at the quantum limiL Semicond. Sci. Tech. 8(1S), S417 (1993)... 

Basic properties of semiconductors and phenomena occurring at the semiconductor/electrolyte interface in the dark have already been discussed in Sections 2.4.1 and 4.5.1. The crucial effect after immersing the semiconductor electrode into an electrolyte solution is the equilibration of electrochemical potentials of electrons in both phases. In order to quantify the dark- and photoeffects at the semiconductor/electrolyte interface, a common reference level of electron energies in both phases has to be defined. 

Photoeffects at the semiconductor/RbAg Is interface were investigated with the objective of identifying the utility of this solid electrolyte material in solid-state photoelectrochemical devices with storage. 

Figure 12.21 shows the effect in an n-type semiconductor of promotion of electrons by incident photons and subsequent electrode reactions. This figure should be compared with Fig. 6.9 for an n-type semiconductor without incident radiation. Irradiation facilitates oxidation, a significant overpotential being unnecessary. Figure 12.22 compares schematically what is obtained at semiconductor electrodes with and without incident light. As is to be expected there is no photoeffect (except in rare cases) for potentials more negative than Uft,. 

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