Dopant ions, sources

Imaging SIMS. Steeds et al. (1999) included this technique in their study of the distribution of boron introduced into diamond, where it is a well-established dopant that controls the electrical conductivity. SIMS was performed with a field-emission liquid gallium ion source interfaced to a magnetic sector mass spectrometer capable of about 0.1 pm spatial resolution. 

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... 

Lewis acid-induced polymerization is also a relatively convenient means to obtain conducting polymers. As with anodic electropolymerizations, monomers are oxidized by an external source, but in this instance electron transfer occurs from the monomer or growing chain to the chemical oxidant. Of the various Lewis acids that are readily available, FeCl3 has become the most popular choice given its effectiveness and low cost. Scheme 7 shows a typical polymerization where the resulting polymer is obtained in its conducting state with FeCl4" dopant ions. 

Ion beam processing provides an alternative and non-equilibrium method of introducing dopant atoms into the lattice. In typical applications, a beam of dopant ions is accelerated through a potential of 10-100 kV. The implantation system shown in Fig. 1.1 illustrates the basic elements required in this technique ion source, acceleration column, mass-separator, and target chamber. With different types of ion sources available, a wide variety of beams may be produced with sufficient intensity for implantation purposes for integrated circuit technology 10 " -10 ions cm (less than a monolayer see Sect. 1.4) is a representative ion dose. Ion dose is defined as the number of ions cm implanted into the sample. Alternatively, the term fluence is used instead of dose. The ion beam current density is expressed in units of A cm . The dose rate or flux is given in units of ions s cm . ... 

In companion publications, pesticides were sampled with a laser desorbed vapors were passed into a differential mobility spectrometer (DMS). Fast detection of pesticides was made using apples, grapes, tomatoes, and peppers, with detection limits in the nanogram range. The detection of pesticides was improved for DMS with an atmospheric pressure photoionization ion source modified with dopants such as benzene, anisole, and chlorobenzene. Improvements of detection limits up to two orders of magnitude were observed, and peaks were displaced on the compensation voltage (CV), axis as expected with modified gas atmospheres in DMS. 

A last example of IMS methods applied to food quality is the determination of aflatoxins B1 and B2 on pistachio samples methanol extracts of samples were introduced into an IMS analyzer equipped with an IMS equipped with a nonradioactive, corona discharge ion source. The response to aflatoxins was acceptable for screening purposes, with a linear range of roughly 100, relative standard deviations 10% or lower, and a limit of detection of 0.25 ng for both aflatoxins. Ammonia could be used as a dopant, and detection limits were improved by a factor of 2.5. Authentic pistachio samples were analyzed without difficulties. 

Table 1.1 shows a list of dopant ions and their source electrolytes which are currently being used in the electrochemical synthesis of conducting polymers. All of these dopant ions with the exception of the last two (marked by ) are anions and are associated with electrochemical oxidation of the polymers at the anode. Aizawa et al. [104] reported the first example of the reductive doping of an electrochemically synthesized polythioenylene film with cations like tetraethyl ammonium (Et4N" )... 

Table 1.1 List of dopant ions and their source of electrolyte (Reprinted from Materials Chemistry and Physics, 61, K. Gurunathan, A. V. Murugan, R. Marimuthu, U. P. Mulik, D. P. Amalnerkar, 173. Copyright (1999) with permission from Elsevier.)...

A measure of the range of influence of the source and drain is the depletion-layer width of the associated p-n junctions. The depletion layer of such a junction is the region in which all carriers have been depleted, or pushed away, due to the potential drop across the junction. This potential drop includes the applied bias across the junction and a spontaneous built-in potential drop induced by spontaneous charge exchange when p- and -regions are brought into contact. The depletion-layer width VT of an abrupt junction is related to potential drop V and dopant-ion concentration/unit volume N by... 

So far we have only considered the case of abrupt junctions where dopant concentration changes abruptly across the interface. Example of this type is when the doping material is implanted into the substrate by means of a high-energy ion source and then annealed at high temperatures over a relatively short period. On the other hand, heating for long period of time... 

The primary sources of contamination in ion implantation come from metal atoms that may be etched off reactor fixtures, such as reactor wads, wafer holder, cHps, and so on. The pump oils used by the vacuum pumps may be a source of hydrocarbon contamination. The dopant sources themselves are not a significant source of contamination because unwanted ions are separated out from the beam during beam analysis. 

The term solid-state laser refers to lasers that use solids as their active medium. However, two kinds of materials are required a host crystal and an impurity dopant. The dopant is selected for its ability to form a population inversion. The Nd YAG laser, for example, uses a small number of neodymium ions as a dopant in the solid YAG (yttrium-aluminum-gar-net) crystal. Solid-state lasers are pumped with an outside source such as a flash lamp, arc lamp, or another laser. This energy is then absorbed by the dopant, raising the atoms to an excited state. Solid-state lasers are sought after because the active medium is relatively easy to handle and store. Also, because the wavelength they produce is within the transmission range of glass, they can be used with fiber optics. 

Figure 25. Proton conductivity of various oxides, as calculated from data on proton concentrations and mobilities, according to Norby and Larring (the type of dopant is not indicated see ref 187 for source data). The conductivity of oxides with a perovskite-type structure are shown by bold lines, and the conductivity of the oxide ion conductor YSZ (yttria-stabilized zirconia) is shown for comparison, (reproduced with the kind permission of Annual Reviews, http //www.AnnualReviews.org).

A method to convert a region of a p-type HgCdTe body to n-type by the use of ion-etching is presented in EP-A-0062367. A high concentration of mercury is produced from an etched-away part of the body as to act as a dopant source. The method is used to form a detector device. 

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