Photoeffect internal

The fifth consequence of the theory is that the adsorptivity and catalytic activity of a semiconductor are affected by illumination. When a crystal absorbs light waves of photoelectrically active frequencies (i.e., frequencies exciting the internal photoeffect), this leads, generally speaking, to a change... 

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). 

Among the first poly conjugated polymers found to display an internal photoeffect were polyquinazones such as polyacenequinone radicals and aniline black21 ... 

By electron capture (e) or internal conversion, electrons are taken away from inner orbitals and the vacancies are filled with electrons from outer orbitals with resulting emission of characteristic X rays. Electrons may also be emitted by an internal photoeffect. Finally, at least one electron is missing, and this may also cause breaking of the chemical bond. As electron capture leads also to a change of the atomic number (Z = Z — 1), it is not possible to distinguish the effects due to the capture of an electron from those that are caused by the change of Z. In internal conversion, however, the atomic number is not changed, and the chemical effects observed in this... 

Semiconductor detectors use the intemal photo effect". That means that the photons generate electron-hole pairs inside the semiconductor. Theoretically the internal photoeffect works with a quantum efficiency of 1. In practice the quantum efficiency of a good silicon photodiode reaches 0.8 around 800 nm. In photodiodes and photoconductors an electrical field separates the electrons and holes, so that a photocurrent flows through the device when it is illuminated. Of course, the photocurrent caused by a single electron-hole pair is far too small to be recorded directly. Single photons can therefore be detected only if the semiconductor detec-... 

In the treatment of photoconductivity in Sect. 8.4.1, we simply mentioned in passing the primary process the generation of the excess charge carriers using the internal photoeffect. In this section, we will treat the details of this process and choose again as an example the anthracene crystal. 

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