Dopant concentration

In moleculady doped polymers, charge transport is carried out by the hole-transporting molecular dopants, usually aromatic amines. The polymer merely acts as a binder. The hole mobiUty is sensitive to the dopant concentrations. For example, the hole mobiUty of... 

At very high dopant concentrations, transport occurs direcdy between the dopant molecules. The polymer acts only as a binder in most cases. Taking TPD-doped PVK as an example, at low TPD concentrations the hole mobihty first decreases from 3 x 10 cm /Vs to 10 cm /Vs with increasing TPD concentration, because TPD molecules act as hole traps (48,49). At higher TPD concentrations, new direct transport channels between the TPD molecules open up and the hole mobihty increases to lO " cm /Vs for ca 60% TPD doping (Table 1, entries 9—11) (48,49). In this case, there is no evidence for unusual interaction between TPD and PVK that affects the hole transport process. 

The PTCR effect is complex and not fully understood in terms of the grain boundary states and stmcture. Both the PTCR effect and room temperature resistivities are also highly dependent on dopant type and ionic radius. Figure 11 (32) illustrates this dependence where comparison of the PTCR behavior and resistivity are made for near optimum concentrations of La ", Nd ", and ions separately substituted into BaTiO. As seen, lowest dopant concentration and room temperature resistivity are obtained for the larger radius cation (La " ), but thePTCR effect was sharpest for the smallest radius cation (Y " ), reflecting dual site occupancy of the Y " ion. 

Fig. 11. PTC resistivity-temperature characteristics for donor dopants of (- D -) 0.15 mol ( ) 0.15 mol Nd " and (O) 0.24 mol Y " in BaTiO. Dopant concentrations are optimum amounts for each type. AH were prepared as nitrates in the same manner (32).

In favorable cases, dopant concentrations down to lO atoms/cm ... 

Obtaining information on a material s electronic band structure (related to the fundamental band gap) and analysis of luminescence centers Measurements of the dopant concentration and of the minority carrier diffusion length and lifetime... 

As mentioned above, the interpretation of CL cannot be unified under a simple law, and one of the fundamental difficulties involved in luminescence analysis is the lack of information on the competing nonradiative processes present in the material. In addition, the influence of defects, the surface, and various external perturbations (such as temperature, electric field, and stress) have to be taken into account in quantitative CL analysis. All these make the quantification of CL intensities difficult. Correlations between dopant concentrations and such band-shape parameters as the peak energy and the half-width of the CL emission currently are more reliable as means for the quantitative analysis of the carrier concentration. 

All the catalysts used in this work were prepared by conventional impregnation method. The selected dopant concentrations were actually relative to the molar quantity of the Ti02 support. 

All materials will, to some degree, be subject to corrosion and oxidation by their environment, and the critical early stages of attack can often be understood through the use of surface analytical techniques. A similar approach is required to gain an understanding of the fundamental and applied aspects of surface catalysis, which is of great importance in the petrochemical industry. The microelectronics industry has also contributed to the development of modern surface analytical techniques, where there is a necessity to analyse dopant concentration profiles while retaining lateral resolution on the device of better than one micron. 

Fig. 25. Absorption coefficient vs. photon frequency for PITN. The data were obtained in situ during the injection part of the electrochemical doping cycle with (CI04 ) as the dopant. The cell voltages and corresponding dopant concentrations (in mol%) are indicated. Reproduced from [456b],...

The dopant concentration depends both on the isotopic abundance and on the neutron absorption cross-section. For natural Ge, a unit neutron flux produces a Ga and As concentration of [14,15] ... 

In the ionic implantation, a beam of trivalent ions (e.g. B+ ions), is used to produce a p+ layer. Pentavalent ions (e.g. P ions), instead, create an n+ layer. The main advantage of this technique rely in the fact that the ions penetrate the crystal only for a short distance from the surface ( 200nm). The penetration depth depends on the beam energy (25 100keV). Typical doping level is 1018 1019ions/cm3. With such a high dopant concentration, the layer becomes practically a metal. 

In this approach to quantitatively analyzing the distribution of carrier concentrations, it was noted that the spatial length scale of dopant concentration fluctuations was an area for future exploration [207]. It is certainly clear that if each crystallite possessed a different dopant and thus carrier concentration, then this approach would be valid to the extent that the Knight shift followed an nj3 functional dependence as expected for a parabolic band. 

From a practical point of view, the optical detection of possible X—H bonds in hydrogenated samples is performed at LHeT as a better sensitivity is obtained at this temperature because the features are sharper than the ones observed at ambient. The sensitivity of Fourier Transform Spectroscopy (FTS) allows usually a normal incidence geometry of the optical beam. Two kinds of samples are generally used in the hydrogenation studies. The first are thin epitaxial layers (1 to 5 in thickness) with dopant concentrations in the 1017-102° at/cm3 range on a semi-insulating... 

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