Use as semiconductors

Intermetallic compounds with gallium are used as semiconductors. Indium is used to coat other metals to protect against corrosion, especially in engine bearings it is also a constituent of low-metal alloys used in safety sprinklers. The toxicity of thallium compounds has limited the use of the metal, but it does find use as a constituent of high-endurance alloys for bearings. 

Metallic Antimonides. Numerous binary compounds of antimony with metallic elements are known. The most important of these are indium antimonide [1312-41 -0] InSb, gallium antimonide [12064-03-8] GaSb, and aluminum antimonide [25152-52-7] AlSb, which find extensive use as semiconductors. The alkali metal antimonides, such as lithium antimonide [12057-30-6] and sodium antimonide [12058-86-5] do not consist of simple ions. Rather, there is appreciable covalent bonding between the alkali metal and the Sb as well as between pairs of Na atoms. These compounds are useful for the preparation of organoantimony compounds, such as trimethylstibine [594-10-5] (CH2)2Sb, by reaction with an organohalogen compound. 

Sulfur vapor consists of a mixture of species that includes S8, S6, S4, and S2 (which like 02 is paramagnetic). Because the S8 molecule is nonpolar, it is soluble in liquids such as CS2 and C6H6. Selenium also consists of cyclic molecules that contain eight atoms, and tellurium is essentially metallic in character. In their vapors, several species are found that contain 2, 6, or 8 atoms. Both are useful as semiconductors, and selenium has been used in rectifiers. Because the electrical conductivity of selenium increases as the intensity of illumination increases, it has been used to operate electrical switches that open or close as a light beam is broken. Selenium was also used in light meters, but other types of meters are now available that are more sensitive. Table 15.1 gives a summary of the properties of the group VIA elements. 

Uses. The unalloyed metal cannot be directly used owing to its bad mechanical properties and its high oxidability. Several thallium alloys are used as semiconductors or ceramic compounds it may be used as additive to gold, silver or copper contacts in the electronic industries. Thallium is dangerously toxic. 

Silicon s tetravalent pyramid crystalline structure, similar to tetravalent carbon, results in a great variety of compounds with many practical uses. Crystals of sihcon that have been contaminated with impurities (arsenic or boron) are used as semiconductors in the computer and electronics industries. Silicon semiconductors made possible the invention of transistors at the Bell Labs in 1947. Transistors use layers of crystals that regulate the flow of electric current. Over the past half-century, transistors have replaced the vacuum tubes in radios, TVs, and other electronic equipment that reduces both the devices size and the heat produced by the electronic devices. 

Bismuth antimonide (BiSb) is not really a compound but single crystals of the alloy of bismuth and antimony. The crystals are used as semiconductors in the electronics industry and to produce type for printing presses and low-melting-point electrical fuses. 

As previously noted, the dielectric constant, e (ASTM D-150-74), is the ratio of the capacity of a condenser made with or containing the test material compared with the capacity of the same condenser with air as the dielectric. Polymers employed as insulators in electrical applications should have low dielectric constants, while those used as semiconductors or conductors should have high dielectric constants. 

The applications of silicon in the electronics industry are so important that the major part of this report will be devoted to the electrochemistry of the elemental silicon crystals used as semiconductors. In fact, the extremely efficient surface treatment of Si wafers needed for the construction of ultra large-scale... 

In investigations by the authors (4) and Li et al. (5), polythieno[3,2-b]thio-phenes, (II) and (III), respectively, were prepared and used as semiconductors and in electronics as organic thin-film transistors. 

Pol y(th iophene-co-selenophcnc) derivatives, (IV), were previously prepared by the authors (6) and used as semiconductors or charge-transport materials. 

Research Focus Synthesis of poly(4,8-didodecyl-2,6-bis-(3-methyl-thiophen-2-yl)-benzo[l,2-b 4,5-b ]dithiophene) derivatives for use as semiconductors in... 

Semiconductor A generic term for a device that controls electrical signals. It specifically refers to a material (such as silicon, germanium or gallium arsenide) that can be altered either to conduct electrical current or to block its passage. Carbon nanotubes may eventually be used as semiconductors. Semiconductors are partly responsible for the miniaturization of modem electronic devices, as they are vital components in computer memory and processor chips. The manufacture of semiconductors is carried out by small firms, and by industry giants such as Intel and Advanced Micro Devices. 

Fig. 4 Molecular structures of the monomeric phthalocyanines used as semiconductors of p-type OFET...

Fig. 7 Molecular structures of monomeric porphyrins used as semiconductor of OFETs...

Fig. 8 Molecular structures of some phthalocyanines used as semiconductors of n-type OFETs...

Silicon is obtained in the ordinary commercial form by reduction of Si02 with carbon or CaQ in an electric furnace. Similarly, Ge is prepared by reduction of Ge02 with C or H2. Silicon and Ge are used as semiconductors in transistors and for microcircuitry and for this reason their properties, including surface chemistry, have been studied extensively.10 Exceedingly high purity is essential, and special methods are required to obtain usable materials these include fractional distillation... 

Polymers having a central core consisting of [2,3-b]-thienothiophene were prepared having a M > 6000 daltons and M > 9000 daltons and used as semiconductors or charge transport materials in electronic devices. By varying the aromatic or ahphatic content of this material, a X ax between 380 and 462 nm was obtained. 

Crosslinkable mesogenic azulenes, (III) and (IV), prepared by Farrand [4], and anthracenyl, (V), and tetracenyl, (VI), thiophenes, prepared by Gerlach [5], were used as semiconductors and charge transport agents in electronic devices. 

Trimeric thiophenes attached to a core-sheU structure, (VII), were prepared by Kirchmeyer [6] and used as semiconductors. 

Polymers and elastomers comprising at least one 9-H,H-fluorene group and at least one arylene group have been prepared. These materials are suitable for use as semiconductors or charge transport materials in optical, electrooptical, or electronic devices, including field-effect transistors, electroluminescent, photovoltaic, and sensor devices. 

In an earlier investigation by the author [2] poly(phenylene-co-vinylene) containing 2,5-thienylene vinylene, (I), was prepared and used as semiconductors in luminescent devices. 

Applications. Some applications of polysilanes include their use as semiconductors, photoresists, photoinitiators, nonlinear optical materials, and ceramic precursors (9). Their use as ceramic precursors can be illustrated by the following reactions ... 

The compounds of groups IIB-IVB are often prepared in poiycrystaliine form as phosphors, catalysts (15.2.2.2) and infrared transmitting materials. Their use as semiconductors is almost exclusively for optoelectronic purposes (i.e., light emission and detection). Thus the phosphor preparation technology has relevance to preparation of these semiconductors in powder form. The most common reactions employed are... 

Use The metal has no significant commercial uses. Its compounds are used as semiconductors. 

Copolymers of dibenzosilole and thiophene have also been used as semiconductors for OFET [37]. Carrier mobilities approaching 0.1 cm2/Vs have... 

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