Intrinsic semi-conductor

Dual-valency Intrinsic Semi-conductors. There is some justification for distinguishing certain compounds of the ionic and molecular ionic type, which have some of the properties associated with defect solids and yet are perfectly stoicheiometric and have insignificant structural defect. They are closely related to some of the other classes of defect solids, W are unique in their compositional and structural perfection. Their properties may be said to arise from an electrical defect ions of the same elements in two different valence states are present in the crystal in stoicheiometric proportions. 

Fig. 5.17. Idealized representations of N(E) as a function of E in different solids (a-d) metals (e) an insulator (/) an intrinsic semi-conductor.

Conducting liquid crystals. Several approaches have been tried, more or less successfully, based also on a 1-D stacking. One of the firsts has been to prepare a liquid crystal based on a phthalocyanine as an intrinsic semi-conductor [83]. One other attempt has been to use discotic liquid crystals, based on the triphenylene molecule oxidized by bromine [84] or by aluminium trichloride [8] in the latter, the conductivity changes by six orders of magnitude (from 10" cm- to 10 cm-i), while the mesomorphic character is conserved. 

Another genre is the so-called homotype impurity system. One example is the substance, nickelous oxide, which is a pale-green insulator when prepcired in an inert atmosphere. If it is reheated in air, or if a mixture of NiO and Li+ is reheated in an inert atmosphere, the NiO becomes a black semi-conductor. This is a classical example of the effect of defect reactions upon the intrinsic properties of a soUd. The defect reactions involved are ... 

Semi-conductors have conducting properties between those of insulators and conductors. The band structures of conductors, intrinsic semiconductors and insulators are represented schematically in Figure 1.4. The widths and the separations of the bands are dependent upon the intemuclear spacings of the constituents, so that the band structure may be modified in the vicinity of the surfaces of the crystal, by the occurrence of surface reactions, or by interactions with gases, liquids or other solids. 

Through a comprehensive review of the recent conductive polymer literature, it has been demonstrated that photoelectron spectroscopy provides a very unique and powerful tool for analyzing the intrinsic structure, the charge transfer interaction, and the stability and degradation behaviour of electroactive polymers. It is further demonstrated that photoelectron spectroscopy is also ideal for investigating the chemistry and electronic structure of the electroactive polymer interface with other polymers, semi-conductors, and metals. The surface and interfacial analytical capability of photoelectron spectroscopy can be further extended to include molecular specificity when coupled with the SIMS technique. Finally, the imaging XPS technique is fast becoming widely available [368]. 

Colloid properties are intrinsic and extrinsic, the first being e.g. chemical behavior, ionization potential or crystallographic structure, the second collective phenomena such as electron gas and lattice resonance. The scheme of electron-energy-levels highly dependent on cluster size and cluster shape is often cited as based on a quantum-size effect. Still most of the behavior of isolated and assembled metal nanoparticles could be deduced from the classic electromagnetic theory without any use of quantum behavior or statistic (Figure 5). Only ultra-small or semi-conductor clusters are not readily described by collective phenomena due a the well-defined assembly of atoms in nano-crystals or due the low number of electrons respectively. 

Contrary to metal and semi-conductor surfaces which present many intrinsic reconstructions, most observed reconstructions on oxide surfaces may be assigned either to an ordering of oxygen vacancies, characteristic of a surface sub-stoichiometry, or to a manifestation, at the surface, of a structural change in the bulk of the material. 

We refer to the intrinsic semi-conductivity. On closer examination of the values of Eg for a certain number of semi-conductor oxides or carbides (see Table 11.1) we can see that the concentrations of electrons and holes may be significant only at veiy high temperatures, unlike what we see for more traditional semi-conductors like silicon... 

Their synthesis has motivated experimental progress in understanding the intrinsic shape-dependent properties of metal and semi-conductor nanocrystals. 

The low intrinsic carrier density of GaAs in a pure (undoped) form indicates that GaAs is intrinsically a very poor conductor and is commonly referred to as being semi-insulating. This property allows many active... 

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