Semiconductors properties

For discussion of electrical conductivity, see Sec. 3.1 of Ch. 4. As opposed to the transition metal carbides, the covalent carbides are considered electrical insulators since they have no metallic bonding and their electrons are strongly bonded to the nucleus and are not free to move. 

Silicon carbide has self-heating and beta-emitting glow characteristics and as such is a standard material for heating elements (see Ch. 15). The anisotropy of the electrical conductivity of boron carbide is low, between 70 and 700 K.0 1 

In a semiconductor material, the forbidden-energy gap is such that electrons in usable quantities are able to jump across it from the filled valence band to the empty eonduction band.1 1 The three elements that form the covalent carbides, i.e., boron, silicon, and carbon (in the form of doped diamond) are semiconductors and one would expect to find semiconductor properties in their compounds. 

Property and Unit Silicon GaAs pSiC Diamond 

Saturated Drift Velocity (em/sec) 1.0x10 2.0x10 2.5xl0 2.7xl0  

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Phthalocyanines have been used to incorporate semiconductor properties in polymers (182) or to develop a thin-film transistor (183). Phthalocyanines and their derivatives can act as dyes in color photography (qv) (184) or electrophotography (185). Light-sensitive compositions for use on Hthographic plates are comprised in part of copper phthalocyanine blue (186). Dichlorosilicon phthalocyanine [19333-10-9] has been used in the... 

Bina Selenides. Most biaary selenides are formed by beating selenium ia the presence of the element, reduction of selenites or selenates with carbon or hydrogen, and double decomposition of heavy-metal salts ia aqueous solution or suspension with a soluble selenide salt, eg, Na2Se or (NH 2S [66455-76-3]. Atmospheric oxygen oxidizes the selenides more rapidly than the corresponding sulfides and more slowly than the teUurides. Selenides of the alkah, alkaline-earth metals, and lanthanum elements are water soluble and readily hydrolyzed. Heavy-metal selenides are iasoluble ia water. Polyselenides form when selenium reacts with alkah metals dissolved ia hquid ammonia. Metal (M) hydrogen selenides of the M HSe type are known. Some heavy-metal selenides show important and useful electric, photoelectric, photo-optical, and semiconductor properties. Ferroselenium and nickel selenide are made by sintering a mixture of selenium and metal powder. 

Tellurium Sulfide. In the hquid state, teUurium is completely miscible with sulfur. The Te—S phase diagram shows a eutectic at 105—110°C when the sulfur content is 98—99 atom % (94—98 wt %). TeUurium—sulfur aUoys have semiconductor properties (see Semiconductors). Bands attributed to teUurium sulfide [16608-21 -2] TeS, molecules have been observed. 

Tellurium Selenides. TeUurium selenides or selenium teUurides are unknown. The molten elements are miscible in aU proportions. The mixtures are not simple soUd solutions but have a complex stmcture. Like the sulfides, the selenides exhibit semiconductor properties. 

Antimony is also used as a dopant in n-ty e semiconductors. It is a common additive in dopants for siHcon crystals with impurities, to alter the electrical conductivity. Interesting semiconductor properties have been reported for cadmium antimonide [12050-27-0] CdSb, and zinc antimonide [12039-35-9] ZnSb. The latter has good thermoelectric properties. Antimony with a purity as low as 99.9+% is an important alloying ingredient in the bismuth teUuride [1304-82-17, Bi Te, class of alloys which are used for thermoelectric cooling. 

The intermetallic compounds with Group 16 (VIA) elements including CdS, CdSe, and CdTe have interesting semiconductor properties for photoconductors, photovoltaic cells, and ir windows. Cadmium sulfide is widely used as a phosphor in television tubes. 

H. J. Queisser. AppL Phys. 10,275, 1976. Describes PL measurements of a variety of semiconductor properties. 

Moreover, it has been established that dehydrocondensation can also be applied to 3,5-diethynyl-l-methylpyrazole, which makes it possible to produce polymer (88%) with an extended system of conjugate bonds possessing semiconductor properties (2001UP2). 

The catalytic activity of PCSs results from their semiconductor properties. The first studies in this field date from 1959—1961. Thus, we have demonstrated catalytic activity of products of the thermal transformation of PAN in the decomposition reactions of hydrogen peroxide, hydrazine hydrate, and formic acid270, 271. There is an indication of catalytic activity of poly(aminoquinone) in the reactions of the hydrogen peroxide decomposition272. ... 

Semiconductor properties are imparted by doping its structure with boron, phosphorus, or arsenic atoms. Silicon is relatively inert chemically but is attacked by halogens and dilute alkalies. It has good optical transmission especially in the infra-red. 

The two covalent carbides have low density, low atomic weight, and useful semiconductor properties. They are extremely hard and strong materials which exhibit typical ceramic characteristics. 

The molar ratio of the III compound to the V compound is typically l/lO.t ] To obtain the desired semiconductor properties, dopants are added such as zinc (from diethyl zinc) or magnesium (from bis(cyclopentadienyl) magnesium) for p doping, and silicon (from silane) or selenium (from hydrogen selenide) for n doping. 

The semiconductor properties of a material shown above can be summarized in two figures of merit shown in Table 13.3. 

The III-V and II-VI compounds refer to combination of elements that have two, three, five, or six valence electrons. They have semiconductor properties and are all produced by CVD either experimentally or in production. The CVD of these materials is reviewed in Ch. 12. Many of their applications are found in optoelectronics where they are used instead of silicon, since they have excellent optical properties (see Ch. 15). Generally silicon is not a satisfactory optical material, since it emits and absorbs radiation mostly in the range of heat instead of light. 

Optoelectronics is a discipline which combines optics and electronics. It deals with optical wavelengths from 0.20 im (ultraviolet) to 3 im (near infrared) as shown in Fig. 15.1. The properties of optoelectronic materials are a useful combination of electrical and semiconductor properties (electron action), with optical properties such as transmission, reflection, and absorption (phonon action). 

A major and growing use of the minor metalloids is in semiconductor fabrication. Germanium, like silicon, exhibits semiconductor properties. Binary compounds between elements of Groups 13 and 15 also act as semiconductors. These 13-15 compounds, such as GaAs and InSb, have the same number of valence electrons as Si or Ge. The energy gap between the valence band and the conduction band of a 13-15 semiconductor can be varied by changing the relative amounts of the two components. This allows the properties of 13-15 semiconductors to be fine-tuned. 

The most prevalent modification of the disulfide, FeS2, is pyrite, which may be visualized as a distorted NaCl structure where the Fe atoms occupy sodium positions and S2 groups are placed with their centers at the chloride positions. Pyrite is a largely occurring crystal with semiconductor properties Eg = 0.95 eV). Another modification of FeS2 is the very similar to pyrite but somewhat less regular marcasite structure. 

The binary chalcogenides of antimony and bismuth are highly colored compounds that are readily prepared by direct reaction of the elements at 500-900 C. They have rather complex ribbon or layer structures and exhibit semiconductor properties. 

These compounds contain a developed system of conjugated double bonds imparting distinct semiconductor properties on them. Metal ions of variable valency can serve as the central ion M cobalt, nickel, iron, manganese, copper, and so on. In such systems, electron transitions can occur in the conjugated system of the ligands and in the electronic system of the central metal ion. These transitions are the basis for their catalytic activity toward various reactions. 

Vladimir I. Veselovsky studied the photoelectrochemical behavior of metals covered with oxide layers having semiconductor properties. In 1955, Walter H. Brattain and Charles G. B. Garrett published a paper in which they established the connection between the photoelectrochemical properties of single-crystal semiconductors and their electronic structure. 

Meier, H. Application of the Semiconductor Properties of Dyes Possibilities and Problems. 61, 85-131 (1976). 

Volume 26 III-V Compound Semiconductors and Semiconductor Properties of Superionic Materials... 

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