Intrinsic region

Therefore, the conductivity in this intrinsic region on the left-hand side of the plot is given by ... 

Because Raman scattering involves vibrational and rotational modes within a sample, its explanation must necessarily involve a quantum mechanical treatment [21]. This is certainly true when the incident light corresponds to an intrinsic region of absorption in the sample, but it is also required for a quantitative analysis of the simpler Stokes and anti-Stokes Raman scattering, which is the subject of the discussion in this chapter. A detailed quantum mechanical understanding of Raman scattering, however, is not necessary for the applications that are of interest in this book, and for that reason, only a brief account is offered here. 

To obtain high counting efficiencies for y or X rays, thick depleted layers (thick intrinsic regions) are needed. These are obtained by drifting Li into crystals of Ge or Si. Ge(Li) crystals are used as detectors for y rays, because of the high density of Ge,... 

For spectrometry, semiconductor detectors with a thickness of the intrinsic region exceeding the maximum penetration distance of the electrons to be counted are suitable. Because of the continuous energy distribution of fi particles, the spectrum of a pure ji emitter is a curve with a maximum at medium energies and extending to a maximum energy max (Fig. 5.7), whereas conversion electrons give relatively sharp peaks. Some pure P emitters are listed in Table 7.5. 

A major disadvantage of the Si(Li) counter is that it must be operated at the temperature of liquid nitrogen (77°K = — 196°C) in order to minimize (1) a constant current through the detector, even in the absence of x-rays, due to thermal excitation of electrons in the intrinsic region, and (2) thermal diffusion of lithium, which would destroy the even distribution attained by drifting. Even when not... 

Klein C, Butt SJ, Machold RP, Johnson JE, Fishell G (2005) Cerebellum- and forebrain-derived stem cells possess intrinsic regional character. Development 132 4497-4508... 

Figure 8.29. Substitutional doping in glow discharge a-Si H (a) Changes in room temperature d.c. conductivity by doping with P and B. Intrinsic region is marked as defect-controlled (b) d.c. conductivity activation energy AEg (= E,/ ) is shown for the dopants (After Spear and Le Comber 1976).

The so-called intrinsic region, where the concentration of impurities is relatively small and the content of thermally induced vacancies is, in contrast, relatively high. In this case, the electroneutrahty condition can be approximated by... 

Figure 3 shows the temperature dependence of the electrical resistivity for the samples from 350K to HOOK in logarithmic scale. The start of intrinsic region can be obtained in the temperature range from 970K to lOOOK... 

The tendency which has the increment of the electrical resistivity with temperature indicates that the scattering mechanism is dominant similar to the behavior of the Seebeck coefficient. In the intrinsic region the characteristic for each sample is not so different from each other. 

Figure 7.22 (a) During the diffusion of lithium, the donor concentration changes with depth as shown, (b) During drifting (at elevated temperature and under reverse hias), and almost intrinsic region is formed with thickness Xq. 

EXAMPLE 7.2 How long will it take to obtain an intrinsic region of 1.5 mm in a silicon wafer drifted at 150° C under a reverse bias of 500 V ... 

Figure 8.30 The Si(Li) semiconductor detector, (a) Schematic shows the n-type Si region on one end of the Si crystal, a central charge depleted intrinsic region and p-type Si on the other end. (b) The actual detector has 200 A layers of gold as electric contacts on each end of the crystal. An X-ray photon striking the intrinsic region generates electron-hole pairs within the diode. [Fig. 8.30(b) courtesy of Thermo ARL (www.thermoARL.com).]...

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