Photogenerated charge

Houle F A 1989 Photochemical etching of silicon the Influence of photogenerated charge carriers Phys. Rev. B 39 10 120-32... 

Fig. 11. Cutaway view of a CCD shift register where the ( ) represent gate electrodes. Voltage pulses appHed to the phase gates move photogenerated charge in the charge-transfer direction. The channel stops confine the charge during integration and transfer. See text.

Microwave measurements are typically performed at frequencies between 8 and 40 Gc/s. The sensitivity with which photogenerated charge carriers can be detected in materials by microwave conductivity measurements depends on the conductivity of the materials, but it can be very high. It has been estimated that 109-1010 electronic charge carriers per cubic centimeter can be detected. Infrared radiation can, of course, also be used to detect and measure free electronic charge carriers. The sensitivity for such measurements, however, is several orders of magnitude less and has been estimated to be around 1015 electronic charge carriers per cubic centimeter.1 Microwave techniques, therefore, promise much more sensitive access to electrochemical mechanisms. 

In the following section the mathematical derivation of the stationary, potential-dependent, photoinduced microwave conductivity signal, which integrates over all photogenerated charge carriers in the semiconductor interface, is explained. This is a necessary requirement for the interpretation of the PMC-potential curves. 

In this chapter we have attempted to summarize and evaluate scientific information available in the relatively young field of microwave photoelectrochemistry. This discipline combines photoelectrochemical techniques with potential-dependent microwave conductivity measurements and succeeds in better characterizing the behavior ofphotoinduced charge carrier reactions in photoelectrochemical mechanisms. By combining photoelectrochemical measurements with microwave conductivity measurements, it is possible to obtain direct access to the measurement of interfacial rate constants. This is new for photoelectrochemistry and promises better insight into the mechanisms of photogenerated charge carriers in semiconductor electrodes. 

Photorefractivity is a property exhibited by some materials in which the redistribution in space of photogenerated charges will induce a nonuniform electric space-charge field which can, in turn, affect the refractive index of the material. In a new material the active species is a highly efficient cyclopalladated molecule97,98 shown in Figure 5. The palladium-bonded azobenzene molecule is conformationally locked, and gratings derived from cis—trans isomerizations can be safely excluded. 

A characteristic property of these different modes is their spatial resolution. A spatial resolution in the order of the illumination wavelength used can be obtained if lateral diffusion of the photogenerated charge carriers is suppressed. This is not the case in mode 2, or in mode 4 if the electrode is under inversion (with J>JPS). If the electrode is kept under depletion as in modes 3 or 4 (with J[Pg.73]

A series of competing processes arise from photogenerated charge carriers in a semiconductor nanoparticle since a large percentage of the atoms are at the surface and behave differently than those in the bulk. An exciton at the surface is rapidly (picosecond) trapped due to surface defects, with the electron-hole pair subsequently participating in transfer between the semiconductor nanoparticle and the electrolyte adsorbed on its surface ... 

Lubberhuizen WH, Vanmaekelbergh D, Van Faassen E (2000) Recombination of photogenerated charge carriers in nanoporous gallium phosphide. J Porous Mater 7 147-152... 

The photorefractive effect is the term used for the changes induced in the refractive index of a material by a redistribution of photogenerated charges. 

---