Hole carrier

Global AMI.5 sun illumination of intensity 100 mW/cm ). The DOS (or defect) is found to be low with a dangling bond (DB) density, as measured by electron spin resonance (esr) of - 10 cm . The inherent disorder possessed by these materials manifests itself as band tails which emanate from the conduction and valence bands and are characterized by exponential tails with an energy of 25 and 45 meV, respectively the broader tail from the valence band provides for dispersive transport (shallow defect controlled) for holes with alow drift mobiUty of 10 cm /(s-V), whereas electrons exhibit nondispersive transport behavior with a higher mobiUty of - 1 cm /(s-V). Hence the material exhibits poor minority (hole) carrier transport with a diffusion length <0.5 //m, which puts a design limitation on electronic devices such as solar cells. 

The low efficiencies could be due to lack of intimate contact (interface) between the sensitizer (which is hydrophilic) and the spirobifluorene (which is hydrophobic). Moreover, the surface charge also plays a significant role in the regeneration of the dye by the electrolyte.98 In an effort to reduce the charge of the sensitizer and improve the interfacial properties between the surface-bound sensitizer and the spirobifluorene hole-carrier, amphiphilic heteroleptic ruthenium(II) complexes ((48)-(53)) have been used as sensitizers. These complexes show excellent stability and good interfacial properties with hole-transport materials, resulting in improved efficiencies for the solar cells. 

L.-S. Yu and S.A. Chen, Full-range tunability of electron and hole carrier mobilities and density ratios via incorporation of highly electron-deficient moieties in poly(phenylene vinylene) side chains, Adv. Mater., 16 744-748, 2004. 

As stated already in the introductory section, main feature of the carrier transport in the polymer is known to be the multitrapping process of the hole carrier. So, the fundamental equation due to Haering and Adams [6 of the fast retrapping limit (equation (i)) will be used to analyze the results ... 

Various methods are proposed (5, a—g), (6). Among these, the methods in which monomolecular recombination or bimolecular recombination of the carriers are assumed could not be used in our case, because the carrier transport in poly-N-vinylcarbazole is known to be the multi-trapping process of the hole carrier. The values of the trap depthaE of 5°C peak by these several methods are summarized in Tab. 1. Values are widely scattered and it seemed that this is due to the approximations involved in the method of analysis. Our value is calculated by the... 

It seems to be natural to suspect if these excimer forming sites were the effective trapping center also for hole carriers. 

Electro-optical modulators are other examples whose efficiency is enhanced in the presence of ion-radicals. These devices are based on the sandwich-type electrode structures containing organic layers as the electron/hole-injecting layers at the interface between the electrode and the emitter layer. The presence of ion-radicals lowers the barrier height for the electron or hole injection. Anion-radicals (e.g., anion-radicals from 4,7-diphenyl-l,10-phenanthroline—Kido and Matsumoto 1998 from tetra (arylethynyl) cyclooctatetraenes—Lu et al. 2000 from bis (1-octylamino) perylene-3,4 9,10-bis (dicarboximide)s— Ahrens et al. 2006) or cation-radicals (e.g., cation-radicals from a-sexithienyl—Kurata et al. 1998 l,l-diphenyl-2-[phenyl-4-A/,A- /i(4 -methylphenyl)] ethylene— Umeda et al. 1990, 2000), all of them are electron or hole carriers. 

The thermopower or thermoelectric power is the electrostatic potential difference between the high and low temperature regions of a material with an impressed thermal gradient and zero electric current flow. The sign gives an indication of the sign of the charge carriers - positive for hole carriers. 

Figure 3.4(a) displays a pulse obtained during a study of the transport of hole carriers in a-As2Se3. It will be observed that the current in the initial regime (prior to... 

Figure 3.4 Typical transient response characteristic for hole carrier transport in a-As2Sc3 at room temperature. The behavior is displayed with both linear (a) and logarithmic (b) axes of current and time.

If, instead of thermal excitation, a photon of light excites an electron from the valence band to the conduction band, the same situation of electron and hole carriers obtains, and one observes the phenomenon of photoconductivity, useful in photocells and similar devices. 

The Fermi surface of WC was proposed based on magnetoresistance and de Haas-van Alphen data taken under high magnetic fields at low temperatures. WC is a semimetal with equal numbers of electron and hole carriers of 1.5 X 1021/cm3. The Fermi surfaces consist of two electron pockets located at the point A and four hole pockets located at the point L, and at the point K or along the T A axis. These results indicate that the spin-orbit interaction is very important in WC. 

Overview of Unit Operations. To maximize the electron or hole (carrier) mobility and thus device speed, ICs are built in single-crystal substrates. Methods of bulk crystal growth are therefore needed. The most common of these methods are the Czochralski and float-zone techniques. The Czochralski technique is a crystal-pulling or melt-growth method, whereas the float-zone technique involves localized melting of a sintered bar of the material, followed by cooling and, thus, crystallization. 

With this understanding, it is clear that in a given conduction 0 covalent transformation, a decrease or increase in the number of conduction electrons is an essential feature that should be observable in the transport properties. Assuming that the band structure of TiNi consists of a single positive band, a decrease in the number of conduction (free) electrons in the course of Ms —> As is equivalent to an increase in the number of hole carriers as seen in (c). Consequently, the positive Hall coefficient should decrease and is so observed in (b). Because holes contribute to Pauli paramagnetic susceptibility in precisely the same manner [42] as electrons, the paramagnetic susceptibility, %, is expected to rise and is so observed in (d). An increase in the hole carrier, Nh, would result in an increase in the conductivity (lowering in the resistivity) as... 

As already mentioned in Sect. 2, there are two alternative pathways of transmembrane electron transfer (i) direct transfer via electron exchange reactions between the molecules located in the inner and outer monolayers of the membrane, such as reactions (8) and (14), and (ii) carrier-mediated transfer, provided by the diffusion of an electron carrier or a hole carrier from one side of the membrane to the other, such as reaction (26). 

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