Dopant species

In solid state materials, single-step electron transport between dopant species is well known. For example, electron-hole recombination accounts for luminescence in some materials [H]. Multistep hopping is also well known. Models for single and multistep transport are enjoying renewed interest in tlie context of DNA electron transfer [12, 13, 14 and 15]. Indeed, tliere are strong links between tire ET literature and tire literature of hopping conductivity in polymers [16]. 

Dopant species can be codeposited with the Si02 by introducing small amounts of the dopants in hydride or haUde form. P-doped Si02, called P-glass, functions as an insulator between polysiUcon gates and the top metallisation layer of ICs. It is also used as a final passivation layer over devices, and as agettering source (17). 

Conducting polymer composites have also been formed by co-electrodeposition of matrix polymer during electrochemical polymerization. Because both components of the composite are deposited simultaneously, a homogenous film is obtained. This technique has been utilized for both neutral thermoplastics such as poly(vinyl chloride) (159), as well as for a large variety of polyelectrolytes (64—68, 159—165). When the matrix polymer is a polyelectrolyte, it serves as the dopant species for the conducting polymer, so there is an intimate mixing of the polymer chains and the system can be appropriately termed a molecular composite. 

Typically, a source gas such as boron trifluoride [7637-07-2], BF3, is exposed to an ion source that causes the gas to ionize. An analyzer discriminates between all the ionic particles using a magnetic field that can select particles having the correct mass-to-charge ratio to pass through the analyzer to an acceleration tube. The ions are accelerated in the tube and collimated into a beam that is scanned over the substrate wafer. The three primary parameters of any implantation process are the type of dopant species, the accelerating energy used for implantation, and the dose of the source gas. The dose is the total number of ions that enter the wafer. Dose, ( ), can be calculated... 

Dopant. Dopant species may be introduced into the semiconducting substrate at various points in the process and by different means. As mentioned above, some dopant may be added to the molten solution as the single crystal is being grown. Dopant introduced in subsequent steps (see steps 1, 3, 4, and 5, Table I) may be introduced by means of diffusion or ion implantation. 

Fig. 3.12. Micro-Raman spectra in the x(yy)x scattering configuration of several PLD-grown, element-doped wurtzite-structure (0001) ZnO thin films on (0001) sapphire [43,48]. Defect-induced modes are marked by solid vertical lines. The asterisks indicate modes, which seem to occur for specific dopant species only. Excitation with Ar+-laser line A = 514.5 nm and laser power P < 40 mW...

The XPS valence band spectrum of an electroactive polymer/dopant complex can be understood in terms of the known valence band spectra of the monomer and the dopant. Thus, the valence band spectroscopy confirms the core-level results by identifying the monomer and dopant species [15]. 

The thiophene and related families of polymers can be synthesized either chemically or electrochemically. However, most of the XPS studies have focused on complexes synthesized by the latter method. The earlier work of Hotta et al. [101] demonstrated that XPS provides a convenient tool for the determination of both the doping level and dopant species in poly(3-methylthienylene). Considerable discrepancies can be found in the subsequent XPS studies on PTH and its alkyl-substituted complexes. The most important issues are probably the charge distribution and the structure of the oxidized or doped PTH chain. 

A further interesting effect discovered in our laboratories is that the addition of low levels of a second component, or dopant ion, can lead to significant increases in the ionic conductivity [6, 30, 31]. Typically these dopant species, for example, Li, OH , and H" ", are much smaller than the organic ions of the matrix, and since the relaxation times characterizing the motion of these ions are more rapid than those of the bulk matrix itself, these materials may represent a new class of fast ion conductor. The dopant ion effect can be used to design materials for specific applications, for example, Li+ for lithium batteries and H /OH for fuel cells or other specific sensor applications. Finally, we have recently discovered that this dopant effect can also be apphed to molecular plastic crystals such as succinonitrile [32]. Such materials have the added advantage that the ionic conductivity is purely a result of the dopant ions and not of the solvent matrix itself. 

In contrast to interstitial defects, the replacement of lattice atoms with dopant species is referred to as substitutional disorder. Since this type of displacement involves extensive diffusion of solvent and solute atoms, a number of requirements must be satisfied. These are known as the William Hume-Rothery Rulest ... 

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