Dopants ionization

The low ionization efficiency can be boosted by adding a suitable substance, called dopant, at the same concentration level of the analyte [57] (see Ref. [49]).The dopant ionization energy must be lower than 10 eV, the energy of the photons, and is ionized producing a molecular ion ... 

Figure 4.1 Degree of dopant ionization as a function of concentration for boron and aluminum estimated at room temperature. The calculation is based on ionization data from Table 4.1 and an effective hole mass of 1.24 m..

The degree of ionization of donors or acceptors is dependent upon the concentrations of charged species within the semiconductor and upon the temperature. Complete ionization is frequently assumed, and this assumption is reasonable at room temperatures. Gerischer70 presents development of these equations under the condition of incomplete dopant ionization. 

These detectors require a material with an impurity dopant ionization energy corresponding to the wavelength to be detected to satisfy condition 1. Conditions 2 and 3 are given by (4.43) and (4.44), except that here there is only one type of carrier affecting detector performance, and in (4.43) represents the... 

The electrical properties of the titanate-based pyrochlores can be described by point defect models in which the acceptor (A) and donor (D) impurities are compensated by oxide ion vacancies, or oxide ion interstitials, respectively. The principal defect reactions inclnde the redox reaction, Equation (5.67), the Frenkel disorder, Equation (5.57), dopant ionization, intrinsic electronic disorder, Equation (5.60), and the electroneutrality relation. For these compounds the total electroneutrality condition given by Equation (5.55) is, on the one hand, reduced, taking Equation (5.57) into account, and is, on the other hand, extended to include acceptor and donor impurities. In addition, defect association is included explicitly. 

Figure 7.4 Dopant ionization energies as a function of dopant covalent radius relative to Si. Note that the acceptors show much greater variation with size than do donors.

The carriers in tire channel of an enhancement mode device exhibit unusually high mobility, particularly at low temperatures, a subject of considerable interest. The source-drain current is carried by electrons attracted to tire interface. The ionized dopant atoms, which act as fixed charges and limit tire carriers mobility, are left behind, away from tire interface. In a sense, tire source-drain current is carried by tire two-dimensional (2D) electron gas at tire Si-gate oxide interface. 

The impurity atoms used to form the p—n junction form well-defined energy levels within the band gap. These levels are shallow in the sense that the donor levels He close to the conduction band (Fig. lb) and the acceptor levels are close to the valence band (Fig. Ic). The thermal energy at room temperature is large enough for most of the dopant atoms contributing to the impurity levels to become ionized. Thus, in the -type region, some electrons in the valence band have sufficient thermal energy to be excited into the acceptor level and leave mobile holes in the valence band. Similar excitation occurs for electrons from the donor to conduction bands of the n-ty e material. The electrons in the conduction band of the n-ty e semiconductor and the holes in the valence band of the -type semiconductor are called majority carriers. Likewise, holes in the -type, and electrons in the -type semiconductor are called minority carriers. 

Instead of depending on the thermally generated carriers just described (intrinsic conduction), it is also possible to deUberately incorporate various impurity atoms into the sihcon lattice that ionize at relatively low temperatures and provide either free holes or electrons. In particular. Group 13 (IIIA) elements n-type dopants) supply electrons and Group 15 (VA) elements (p-type dopants) supply holes. Over the normal doping range, one impurity atom supphes one hole or one electron. Of these elements, boron (p-type), and phosphoms, arsenic, and antimony (n-type) are most commonly used. When... 

What role does the dopant play in APPI (Ionization of molecules having a low photoionization cross section (probability) has been shown to be enhanced by the use of a dopant that is introduced into the vaporized plume of analyte molecules the dopant is selected on the basis of its high UV absorptivity and serves as a charge transfer reagent). 

Robb, D. B., and Blades, M. W. (2006). Factors affecting primary ionization in dopant-assisted atmospheric pressure photoionization (DA-APPI) for LC/MS. J. Am. Soc. Mass Spectrom. 17, 130-138. 

The in-line source depicted in Figure 8.7 was designed by Bruins et al. to be mounted on a PE-Sciex triple quadrupole and it was derived from the standard heated nebulizer of their APCI source. The corona needle is replaced by a discharge lamp. Nitrogen is used as the nebulizing and the lamp gas, while air is used as the auxiliary gas. A dopant improves the efficiency of ionization and it is supplied through the auxiliary gas line and vaporized together with the solvent in the heated nebulizer. 

In the negative ion mode of the ionization process, an electron is released by the effect of the PI of the dopant ... 

Pioneering work on stable doping in organic LEDs has been carried out by the group of K. Leo in Dresden and has been reviewed by Walzer [107]. It is now clear that F4-TCNQ can act as a dopant because its electron affinity is close to 5 eV [110, 111], which is close to the ionization potential of triphenylamine derivatives and to some phthalocyanines (Pc) [107]. It turns out that doping of ZnPc by 2% of F4-TCNQ raises the conductivity to a level of 10 cm When using TCNQ... 

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