Doping elements

Other single-crystal x-ray diffraction studies of transition element dopants in jS-rh boron are based on the results of a refinement of the /3-rh boron structure that establishes the occurrence of four new low-occupancy (3.7, 6.6, 6.8 and 8.5%) B positions in addition to the earlier known ones. The dopant elements studied, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Hf and Ta, do not enter B positions in the framework, but they enter the Al, A2, D and E positions. In some cases the doping elements have been studied at several concentrations for each element and for different cooling rates. The percentage occupancies of certain positions are eorrelated with the atomie sizes of the dopants. The bond distances between the polyhedra are shorter than those within the polyhedra. The mechanism of doping for some cases is denoted displacive, rather than interstitial or substitutional, because of competing interactions between the six different partially occupied B positions and dopant atoms. 

The analysis of tetramethylammonium hydroxide (TMAH) solutions manufactured by SACHEM Inc. of Cleburne, Texas, includes the determination of trace elements. These elements cause less-than-optimum performance of integrated circuit boards manufactured by SACHEM s customers that use these solutions in their processes. Alkali and alkaline earth metals (e.g., Li, Na, K, Mg, Ca, and Ba) can reduce the oxide breakdown voltage of the devices. In addition, transition and heavy metal elements (e.g., Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag, Au, and Pb) can produce higher dark current. Doping elements (e.g., B, Al, Si, P, As, and Sn) can alter the operating characteristics of the devices. In SACHEM s quality control laboratory, ICP coupled to mass spectrometry is used to simultaneously analyze multiple trace elements in one sample in just 1 to 4 min. This ICP-MS instrument is a state-of-the-art instrument that can provide high throughput and low detection Emits at the parts per thousand level. Trace elemental determination at the parts per thousand level must be performed in a clean room so that trace elemental contamination from airborne particles can be minimized. 

In doped silicon (an extrinsic semiconductor) the doping element has either three or five valence electrons (one electron less or one electron more than the four valence electrons of silicon). Substituting an arsenic or phosphorus atom (five valence electrons) for a silicon atom in a silicon crystal provides an extra loosely-bound electron that is more easily excited into the CB than in the case of the pure silicon. In such an n-type semiconductor, most of the electrical conductivity is attributed... 

Because of the potential importance for industrial-scale catalysis, we decided to check (i) whether an influence of a semiconductor support on a metal catalyst was present also if the metal is not spread as a thin layer on the semiconductor surface but rather exists in form of small particles mixed intimately with a powder of the semiconductor, and (ii) whether a doping effect was present even then. To this end the nitrates of nickel, zinc (zinc oxide is a well-characterized n-type semiconductor) and of the doping element gallium (for increased n-type doping) or lithium (for decreased n-type character) were dissolved in water, mixed, heated to dryness, and decomposed at 250°-300°C. The oxide mixtures were then pelleted and sintered 4 hr at 800° in order to establish the disorder equilibrium of the doped zinc oxide. The ratio Ni/ZnO was 1 8 and the eventual doping amounted to 0.2 at % (75). 

Churilov, G.N., Petrakovskaya, E.A., Bulina, N.V., Marachevsky, A.V., Gryaznova, S.A., Vnukova, N.G., Novikov, P.V. (2004) Composite clusters obtained in carbon-helium plasma at atmospheric pressure by injection of doping elements, Int. Symp. on Carbon of Catalysis, 181-182. 

Pitting or void in the poly-Si is a common mode of defect. The severity of such a defect depends on the type of poly-Si material involved. More specifically, the crystalline structure and the level of doping elements can have a significant impact on the tendency of the poly-Si film to form pits and voids during the CMP process. 

Monk et attributed the role of doping elements in the oxide to the electronic characteristics of the elements. Whether the doped atom is electrophilic or nucleophilic toward the Si atom governs how easily HFJ is coordinated with the Si atom. If the oxide film has an electrophilic dopant, the etch rate increases, and if it is nucleophilic, the etch rate decreases, hi a PSG film the doped P atom, which has a valence of 5, has one valence electron more than Si. This means that a doped oxide can provide the electron to oxygen more easily than can a nondoped one. Therefore, the silicon-oxygen bond in P-doped oxide can be broken more easily. 

Some doping element sources exist as oxides, such as Ga203 and Cr203. These metals are difficult to separate from O, but this can be done in the presence of heat and CT. When such oxides are used with CCI4 for internal chlorination, precise temperature control is not required. 

A variety of solvents have been proposed like Au, Al, Ga [29,30], Pb [31], Sn [32] and others alloys as Au-Pb, Au-Zn, Al-Sn, Al-Zn [33], Au-Bi [32], Al-Ga [34], and Sn-Pb [35]. Resulting layers presented high doping level up to 1018 at. cm-3 (when using doping element like Al, Ga), uncompleted coverage of the surface (non-miscibility of Si in some alloys at low-temperature) or resulted in layers with electrical defects (Au). 

Named after the continent of Europe, europium is part of the complex yttria family of rare earths. It was isolated in 1901 by Eugbne-Anatole Demargay (1852-1904), who also named it. Europium is one of the rarest and most expensive rare-earth elements. In its pure form, it is silvery white and resembles lead. It is used as part of the red phosphor in color televisions and as a doping element for lasers. 

It is therefore advisable to use the doping elements in quantities compatible with complete solubility in the host oxide, and to check that they do not segregate during the catalytic reaction. Cobalt, mentioned above as a useful dopant, could exert a catastrophic effect if segregated as cobalt oxide, because of the high activity of the latter in complete oxidation. 

Fig. 11.9 The prepared sample plate and distribution of the doping elements on the base material CoTi03/La...

The second approach is based on addition of a precious metal or oxide catalyst (Fig. 12.1b). The design of a catalyst usually requires a large number of experiments because various catalyst materials are available and their concentrations should be optimized. In this respect, the combinatorial method is advantageous. Indeed, there are reports on the design of catalysts or surface doping elements that promote the selective gas sensing reaction.48"50... 

---