Silicon high-purity

Finally, in 1985, the results of an extensive investigation in which adsorjDtion took place onto an aluminium oxide layer fonned on a film of aluminium deposited in vacuo onto a silicon wafer was published by Allara and Nuzzo 1127, 1281. Various carboxylic acids were dissolved in high-purity hexadecane and allowed to adsorb from this solution onto the prepared aluminium oxide surface. It was found that for chains with more than 12 carbon atoms, chains are nearly in a vertical orientation and are tightly packed. For shorter chains, however, no stable monolayers were found. The kinetic processes involved in layer fonnation can take up to several days. 

Silicon is used in many fonns, from high-purity tliin films to bulk material, which may be crystalline, multi- or poly crystalline and amorjDhous (usually hydrogenated). Silicon is the material discussed tire most in tliis article. Substitutional B and P are tire most common (of many) shallow acceptors and donors, respectively. 

Silicon reacts at elevated temperatures with the halogens, forming SiCl, Sil, SiBr, and SiF. There is also a series of halogen-substituted silanes such as trichlorosilane, SiH Cl, and dichlorosilane, S1H2CI2. Both SiCl and SiH Cl are relatively easy to make, purify, and reduce to silicon. These are the silicon compounds most often used as feedstocks in the manufacture of high purity silicon. 

The partially alkoxylated chlorotitanates, (RO) TiCl, can be prepared in high purity by reaction of TiCl with an organosilane ester, Si(OR)4 (see Silicon compounds). The degree of esterification of the titanium can be controlled by the amount of silane ester used. When is 3 or 4, the addition of the appropriate alcohol and an amine receptor is required (5). 

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. 

Figure 6 Typical secondary ion mass spectrum obtained from high-purity silicon using an oxygen ion beam. Major ion peaks are identified in the spectrum.

Silicon (96-99% pure) is now invariably made by the reduction of quartzite or sand with high purity coke in an electric arc furnace the Si02 is kept in excess to prevent the accumulation of SiC (p. 334) ... 

With increasing purity of aluminium, greater resistance to corrosion is developed. On high-purity materials, however, any pits which develop are likely to be deeper though fewer in number than those formed in more impure metal. In some special applications, notably in contact with ammonia solutions or pure water at elevated temperatures and pressures, the iron and silicon present in commercial-purity metal are beneficial and retard corrosion. Up to about 5% magnesium improves the corrosion resistance to sea-water. 

Silicon in the elemental state has important electronic applications as a semiconductor that were developed only during the last decade. The discovery of these uses was possible only after methods were developed for preparing silicon of extremely high purity. Reduction of Si02 with... 

The USA Military Specification (Ref 14) contains the following requirements and criteria (1) a pre-production sample must meet the Spec requirements, (2) silicon monoxide shall be of a high purity grade, (3) chemical compn as detd by the powder—D-C arc semiquantitative technique... 

Silicon is the second most abundant element in the Earth s crust. It occurs widely in rocks as silicates, compounds containing the silicate ion, Si032, and as the silica, Si02, of sand (Fig. 14.33). Pure silicon is obtained from quartzite, a granular form of quartz (another solid phase of SiOz), bv reduction with high-purity carbon in an electric arc furnace ... 

The deposition temperature range is 250-600°C and the pressure is up to 20 T orr. T o minimize carbon inclusion, the carbonyl is highly diluted with hydrogen (ratio of 1/100) and high purity deposits can be obtained. PI Reaction (6) has a low temperature reaction and isbeing considered for deposition on silicon and III-V semiconductors. 

P, Pohl, H.-J., Schenkel, T., I hewall, M.L.W., Itoh, K.M. and Lyon, S.A. (2012) Electron spin coherence exceeding seconds in high-purity silicon. Nat. Mater., 11, 143-147. 

Czochralski seeded single-crystal growth from semiconductors stable as melts, which yields the meters-large single crystals of ultra-high purity silicon used in nearly all technological applications. 

In high purity silicon below T = 140 K the Mu center is stable on the time scale of the muon lifetime (2.2 ps). However, in electron irradiated silicon Westhauser et al. (1986) have reported that Mu is metastable and makes a thermally induced transition to Mu at a temperature of 15 K. A similar transition between Mu and Mu was first discovered in diamond (Holz-schuh et al., 1982, Odermatt et al., 1988) and will be discussed in Sec-... 

The treatment assumes that the point defects do not interact with each other. This is not a very good assumption because point defect interactions are important, and it is possible to take such interactions into account in more general formulas. For example, high-purity silicon carbide, SiC, appears to have important populations of carbon and silicon vacancies, and Vsj, which are equivalent to Schottky defects, together with a large population of divacancy pairs. 

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