Arsenic, dopant

Arsenosilicates (AsSG) were employed originally in silicon device technology as an arsenic dopant source for planar substrates prior to the advent of large scale ion... 

FIGURE 40.30 Arsenic dopant distribution in silicon. APT reconstruction showing isoconcentration surfaces of 2 at.% As (lower part, particles) and 10 at.% O (upper part, diskshaped structure). Reprinted from Cerezo, A., Clifton, P.H., Galtrey, M.J., Humphreys, C.J., Kelly, T.F., Larson, D.J., Lozano-Perez, S., Marquis, E.A., Oliver, R.A., Sha, G., Thompson, K., Zandbergen, M., Alvis, R.L.(2007) Atom probe tomography today. Materials Today, 10 2), 36-42. Copyright 2007, with permission from Elsevier. 

EDMR has allowed several different unusual experiments. For example, neutral arsenic dopants interacting with a 2D electron gas have been studied with continuous-wave EDMR at 9.7 GHz and 94 GHz. The Anderson-Mott transition between conduction by sequential tunneling through isolated dopant atoms, and conduction through thermally activated impurity Hubbard bands has been studied in arrays of a few arsenic dopant atoms in a silicon transistor. Single erbium spins with resolved hyperfine structure have been electrically detected after resonant optical excitation. The use of the valley degree of freedom has been eonsidered with dopants in silicon both experimentally and theoretically. The quantum confinement due to silicon nanowires may inerease the temperatures where silicon donor quantum devices ean operate. ... 

The oxidation of methacrolein to methacrylic acid is most often performed over a phosphomolybdic acid-based catalyst, usually with copper, vanadium, and a heavy alkaU metal added. Arsenic and antimony are other common dopants. Conversions of methacrolein range from 85—95%, with selectivities to methacrylic acid of 85—95%. Although numerous catalyst improvements have been reported since the 1980s (120—123), the highest claimed yield of methacryhc acid (86%) is still that described in a 1981 patent to Air Products (124). 

Atoms of elements that are characterized by a valence greater than four, eg, phosphoms or arsenic (valence = 5), are one type of dopant. These high valence dopants contribute free electrons to the crystal and are cabed donor dopants. If one donor atom is incorporated in the lattice, four of the five valence electrons of donor dopants are covalentiy bonded, but the fifth electron is very weakly bound and can be detached by only ca 0.03 eV of energy. Once it is detached, it is available as a free electron, ie, a carrier of electric current. A sibcon crystal with added donor dopants has excess electron carriers and is cabed n-ty e (negative) sibcon (Fig. Ic). 

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... 

Arsenic from the decomposition of high purity arsine gas may be used to produce epitaxial layers of III—V compounds, such as Tn As, GaAs, AlAs, etc, and as an n-ty e dopant in the production of germanium and silicon semiconductor devices. A group of low melting glasses based on the use of high purity arsenic (24—27) were developed for semiconductor and infrared appHcations. 

Uses/Sources. In the electronics industry to manufacture gallium arsenide and gallium arsenide phosphide for semiconductors and as a dopant produced accidentally as a result of generation of nascent hydrogen in the presence of arsenic or by the action of water on a metallic arsenide... 

McLain has reported that potassium chlorate containing 2.8 mole% copper chlorate as an intentionally-added impurity (or "dopant") reacted explosively with sulfur at room temperature [7] A pressed mixture of potassium chlorate with realgar (arsenic sulfide, AS2S2) has also been reported to ignite at room temperature [2]. 

When heated, polyvinyl chloride (PVC) and polyvinyl alcohol (PVA) lose HC1 and H20, respectively, to produce dark-colored conductive polyacetylene. Superior polymers of acetylene can be made by the polymerization of acetylene with Ziegler-Natta catalysts. The conductivity of polyacetylene is increased by the addition of dopants, such as arsenic pentafluoride or sodium naphthenide. 

Elemental forms of gallium and arsenic, plus small quantities of dopant material — silicon, tellurium or chromium — are reacted at elevated temperatures to form ingots of doped single-crystal GaAs. 

For epi depositions with arsenic buried layers, we can see the influence of pressure on dopant profile for the SiCI4 process in Figure 19 and for the SiHjC process in Figure 20. In both cases, as the pressure is reduced, the width of the transition region is less. Measurements were made by SIMS. The heavily-doped buried layer substrate is shown on the right-hand side of these figures, and the epi film is on the left. 

Typical oxidising dopants used include iodine, arsenic pentachloride, iron(III) chloride and NOPF6. A typical reductive dopant is sodium naphthalide. The main criteria is its ability to oxidise or reduce the polymer without lowering its stability or whether or not they are capable of initiating side reactions that inhibit the polymers ability to conduct electricity. An example of the latter is the doping of a conjugated polymer with bromine. Bromine it too powerful an oxidant and adds across the double bonds to form sp3 carbons. The same reaction may occur with NOPF, but at a lower rate. 

Fig. 5.4. The distribution coefficients of arsenic and phosphorus dopants as a function of the rf power in the plasma at different gas phase concentrations (Winer and Street 1989).

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