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Trivalent semiconductors

Low levels of structural Ge" have also been observed in natural hematite from the Apex mine, Utah (Bernstein Waychunas, 1987) and to achieve charge balance, incorporation of two Fe for one Ge", i.e. similar to the two Fe" for one in ilme-nite, has been suggested. Synthetic, single crystals of Ge substituted hematite have also been grown by a chemical vapour transport method (Sieber et al. 1985). A range of elements including Zr, Ge, Hf, V, Nb, Ta, W and Pb has been used as low level dopants (2 10 - 0.2 g kg ) to improve the semiconductor behaviour of hematite anodes (Anderman Kermedy, 1988). The increase in unit cell c from 1.3760 to 1.3791 nm and in a from 0.50378 to 0.50433 nm indicated that Nd (as an inactive model for trivalent actinides of similar ionic size (Am r = 0.0983 nm Nd " r = 0.098 nm)) was incorporated in the structure (Nagano et al. 1999). [Pg.55]

The substitution for Cu by a 3d metal produces drastic changes in the physical properties of the 90K phase, as shown in Figure 9a where the Tc s (as determined by ac-susceptibility measurements)are plotted as a function of x for the various series. Independent of the magnetic nature of the substituted element, for the trivalent ions (Fe, Co, and Al) Tc remains constant and equal to 90K up to the O-T transition and then decreases continuously to less than 4.2K at x-0.5. Upon increasing x further, the compounds become semiconductors and simultaneously antiferromagnetism associated with the Cu ions develops. In contrast to this behavior, for the divalent substituted Ni and Zn ions Tc decreases markedly, even at low x. [Pg.326]

Another, and on the face of it, rather different example, is the coprecipitation of solid solution compounds, such as CulnSi and CulnSei—semiconductors of particular interest due mainly to their applicability for photovoltaic cells. It was shown, by X-ray diffraction, that the precipitate resulting from reaction between H2S and an aqueous solution containing both Cu" and In " ions was, at least in part (depending on the concentrations of the cations), single-phase CulnSi [3]. Two factors were found to be necessary for this compound formation (1) the presence of sulphide on the surface of the initially precipitated colloidal solid metal sulphide and (2) one of the cations being acidic and the other basic. The monovalent Cu cation is relatively basic, while the trivalent In cation is relatively acidic. It is not clear what the physical reason is for this latter requirement. A difference in practice between acidic and basic cations is that, in an aqueous solution of both cations, the acidic cation is more likely to be in the form of some hydroxy species (not to be confused with hydrated cations), while the basic cation is more likely to exist as the free cation. [Pg.292]

The Fermi level is a theoretical energy of electrons in a semiconductor, such that the probability of occupation of the VB and CB is 50%. In an intrinsic semiconductor this Fermi level is about half-way between the VB and the CB, but it can be displaced substantially in doped semiconductors. An intrinsic semiconductor would be for example a crystal of pure Si or Ge, all tetravalent atoms being linked together in a three-dimensional array. In a doped semiconductor of n -type some of the Si atoms are replaced by pentavalent atoms such as As, and these will release electrons into the CB. A p -type semiconductor, however, contains some trivalent atoms like A1 which are electron deficient. The Fermi level moves closer to the CB in the n-doped semiconductor, while it comes closer to the VB in the p-type semiconductor (Figure 3.46). [Pg.74]

Figure 3.45 In a doped semiconductor some tetravalent atoms are replaced by trivalent atoms (p-type) or pentavalent atoms (n-type)... Figure 3.45 In a doped semiconductor some tetravalent atoms are replaced by trivalent atoms (p-type) or pentavalent atoms (n-type)...
Figure 3.46 In a p-type semiconductor the electrons are held by the trivalent atoms and their overall energy (the Fermi level) is lowered. In an n-type semiconductor electrons are released by the pentavalent atoms and the Fermi level comes closer to the conduction band. SC = semiconductor... Figure 3.46 In a p-type semiconductor the electrons are held by the trivalent atoms and their overall energy (the Fermi level) is lowered. In an n-type semiconductor electrons are released by the pentavalent atoms and the Fermi level comes closer to the conduction band. SC = semiconductor...
CeRii4P]2 is a narrow gap semiconductor with a gap of 0.075 eV estimated from electrical transport measurements on polycrystalline samples (Shirotani et al., 1996). XANES measurements indicate trivalent Ce with strong hybridization with ligand orbitals. The gap is presumably formed from the hybridization of the Ce 4f states with the Ru d and P-p orbitals... [Pg.12]

While the diamagnetic AuSb2 is a metallic and even superconducting (27) d7 pyrite, the corresponding Cu and Ag phosphides are both diamagnetic semiconductors (33, 134). The cation, therefore, must be either mono- or trivalent. The monoclinic structure of CuP2 has recently been determined by Olofsson (135) [C h — P2i/c, all atoms in 4(e)], The phosphorus atoms form infinite puckered layers almost identical to those met... [Pg.136]

Solid state detectors consist of three layers, a layer of pure silicon sandwiched between a p-type and an n-type conductor. We recall that an example of an n-type conductor is germanium to which is added P or As, an impurity. The extra electron in the phosphorus or arsenic atoms is thought of as being in an energy level close to the conduction band. These electrons are readily thermally excited into the conduction band increasing the conductivity. A p-type semiconductor may be silicon to which a trivalent element such as boron or aluminum is added as an impurity. This creates holes close to the valence band. Electrons are readily promoted to these holes leaving positive holes in the valence band that provide for a conduction pathway. [Pg.6414]

Photodiode array detectors are an offshoot of semiconductor technology. In semiconductors, impurities have been added to pure silicon to create two classes of materials. The addition of arsenic, bismuth, phosphorous, or antimony creates a pentavalent material (n-type) that is able to function as a donor of electrons. The addition of trivalent elements such as aluminium, boron, gallium, indium, etc., to silicon gives rise to the p-lypc material, in which the trivalent material is able... [Pg.228]

Fig. 11. Lattice constants of monochalcogenides of the RE. We have indicated the value (5.71 A) for metallic SmS at 6.5 kbar, after the first order semiconductor-metal transition. Fully trivalent SmS should have an interpolated lattice constant of 5.61 A. The case of the Tm monochalcogenides is discussed in the text. Fig. 11. Lattice constants of monochalcogenides of the RE. We have indicated the value (5.71 A) for metallic SmS at 6.5 kbar, after the first order semiconductor-metal transition. Fully trivalent SmS should have an interpolated lattice constant of 5.61 A. The case of the Tm monochalcogenides is discussed in the text.

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See also in sourсe #XX -- [ Pg.244 ]




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