Ordinary semiconductors

The thickness of depletion and deep depletion layers may be approximated by the effective Debye length, Lo, ff, given in Eqn. 5-70 Ld, is inversely proportional to the square root of the impiuity concentration, In ordinary semiconductors... 

Fig. 12. Examples of action and pseudo-action spectra for photoin-duced reaction by an ordinary semiconductor photocatalyst (shorter wavelength) and an organic dye (longer-wavelength peak). A pseudoaction spectrum taken by cut-off filters corresponds to integration of the true action spectrum from the longer-wavelength side.

The semiconductor detector is similar to an ordinary semiconductor diode composed of p-type and n-type semiconductor material. This detector has become dominant for nuclear spectroscopy (i.e. determination of the energy of nuclear radiation) but it is not so often used for simple measuremrat of count rates. 

On the other hand, the electrical properties of ice, principally due to the presence of a large number of carriers and the nature of the carriers, may give rise to memory effects which are much more complicated compared with the electrical properties of ordinary semiconductors. Therefore, using ice, one can realize devices which either have no analogues amongst semiconductor devices or which are advantageous compared with the latter. Some such devices are described next. 

The middle frame of fig. 49 shows the most obvious problem, namely that at Q = (0.36, 0, 1.2) there are substantial low-frequency magnetic fluctuations remaining in the insulating regime. Thus, in contrast to an ordinary semiconductor, CeNiSn displays a gap which is well-defined only at particular wavevectors. Another curious result is that while x" Q> is obviously a strong function of Q, the zero-frequency real part of x(Q, tw), defined by the Kramers-Kronig relation. 

One might also ask why it is necessary for an ordinary semiconductor engineer to worry about these details unless they were planning to pursue a graduate degree in semiconductor physics. The reason is that many aspects of semiconductor alloy and defect behaviors can be traced back to the phenomena discussed above. Furthermore,... 

Even though silicon is metallic in appearance, it is not generally classified as a metal. The electrical conductivity of silicon is so much less than that of ordinary metals it is called a semiconductor. Silicon is an example of a network solid (see Figure 20-1)—it has the same atomic arrangement that occurs in diamond. Each silicon atom is surrounded by, and covalently bonded to, four other silicon atoms. Thus, the silicon crystal can be regarded as one giant molecule. 

On the basis of our theoretical considerations and preliminary experimental work, it is hoped that fast processes of charge carriers will become directly measurable in functioning photoelectrochemical cells, Typical semiconductor electrodes are not the only systems accessible to potential-dependent microwave transient measurements. This technique may also be applied to the interfacial processes of semimetals (metals with energy gaps) or thin oxide or sulfide layers on ordinary metal electrodes. 

Photosensitive substances adsorbed on the semiconductor surface are especially efficient in sensitization reactions. Thus, sensitizing effect can be enhanced if a sensitizer is attached to the semiconductor surface by a chemical bond. For this purpose one has to create either the ether bond -O-between the semiconductor and reactant, using natural OH groups, which exist on the surface of, for example, oxide semiconductors (Ti02, ZnO) or oxidized materials (Ge, GaAs, etc.) in aqueous solutions, or the amide bond -NH- in the latter case a monolayer of silane compounds with amido-groups is preliminarily deposited on the semiconductor surface (see, for instance, Osa and Fujihira, 1976). With such chemically modified electrodes the photocurrent is much higher than with ordinary (naked) semiconductor electrodes. 

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). 

Normally, ionic solids have very low conductivities. An ordinary crystal like sodium chloride must conduct by ion conduction since it does not have partially filled bands (metals) or accessible bands (semiconductors) for electronic conduction. The conductivities that do obtain usually relate to the detects discussed in the previous section. The migration of ions may be classified into three types. 

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