Arsenic doping with

Hyperpure silicon can be doped with boron, gallium, phosphorus, or arsenic to produce silicon for use in transistors, solar cells, rectifiers, and other solid-state devices which are used extensively in the electronics and space-age industries. 

Self-Test 3.12A Which type of semiconductor is germanium doped with arsenic ... 

Silicon s atomic structure makes it an extremely important semiconductor. Highly purified silicon, doped with such elements as boron, phosphorus, and arsenic, is the basic material used in computer chips, transistors, sUicon diodes, and various other electronic circuits and electrical-current switching devices. Silicon of lesser purity is used in metallurgy as a reducing agent and as an alloying element in steel, brass, and bronze. 

The semiconductor silicon obtains its remarkable properties upon doping with arsenic. Hence, practically all electronic devices contain this element. 

Arsine is used as a reducing agent and to synthesize many organoarsine derivatives. It is also used as a doping agent for solid state electronic components. Earlier, it was used as a military poison gas. It does not occur freely in nature but is susceptible to form upon contact of arsenic compounds with acid in presence of a metal. Thus commercial acids stored in metal tanks and contaminated with arsenic impurities may produce arsine. 

Sihcon of hyperpurity, doped with trace elements, such as boron, phosphorus, arsenic, and gadium is one of the best semiconductors. They are used in transistors, power rectifiers, diodes and solar ceds. Sihcon rectifiers are most efficient in converting a-c to d-c electricity. Hydrogenated amorphous sihcon converts solar energy into electricity. 

Consider an interface formed by joining together an n-type semiconductor (e.g., germanium doped with arsenic atoms, which donate electrons to the conduction... 

PROBLEM 21.4 Is germanium doped with arsenic an M-type or p-type semiconductor Why is its conductivity greater than that of pure germanium ... 

In 1982, Soga et al. 256> showed that exposure of acetylene to AsFs at low temperatures leads to rapid polymerization (in our experience this reaction can be explosively violent). The product is a solid polymer which is heavily arsenic-doped and has a conductivity several orders of magnitude lower than a conventional sample of polyacetylene saturation-doped from the gas phase. Aldissi and Liepins 2S7) have adapted this reaction to the preparation of soluble polyacetylene by adopting AsF3 as the reaction solvent. They claim that polymerization of acetylene with AsF5 is very rapid, giving a polymer which is soluble in common solvents. However, elemental analysis shows that the polyacetylene formed contains about one As atom per 10 CH units and this is not removed on repeated reprecipitations. It seems likely that the As atoms form part of the chain backbone, conferring sufficient flexibility to allow dissolution. It is claimed that films of soluble polyacetylene can be doped but very little information has been published. 

A semiconductor of the n-type is formed, for example, when silicon is doped with arsenic atoms. The inbuilt arsenic atom uses four valence electrons to bind to the four surrounding silicon atoms (fig. 11.4.7) and the fifth valence electron is not needed for binding to... 

Arsenic Oxidation States. A solution sample was taken 257 hr after initiation of the 300°C basalt + arsenic-doped deionized water experiment (Run D2-8, Table II). The data from arsenic oxidation state AAS analysis of the initial As(V)-doped water (0-hr sample) and of the 257-hr solution sample are given in Table HI. All detectable arsenic was in the +3 oxidation state [As(V) <15pg/L] in the 257-hr sample. Standard additions of AsGD) and As(V) to the 257-hr sample were quantitatively recovered. To desorb arsenic from particulates in this sample, an aliquot of the solution was treated with 5% hydrofluoric acid. The higher As(III) content of the treated 257-hr sample aliquot (110 vs. 61pg/L, Table HI) demonstrates that sorption occurred. Scanning transmission electron microscopic (STEM) analysis of the particulates indicated the presence of poorly crystallized high-iron illite . 

Silicon (Si) Silicon is a lustrous silvery gray material. Because silicon conducts electricity, but not as well as a metal, silicon is classified as a semimetal. Crystals of pure silicon that have been doped with arsenic or gallium are known as semiconductors and are used to fabricate computer chips. Silicone rubbers are polymers containing silicon, oxygen, and various hydrocarbon groups, and are used in applications ranging from sealants to breast implants. 

An n-type (for negative type) semiconductor is an electron rich material comprised of silicon (Group IV) doped with something like arsenic (Group V). Arsenic atoms have one additional valence electron compared to silicon atoms, so the crystalline lattice has more electrons compared to pure silicon. This is shown in Figure 10.14. 

If silicon is doped with arsenic, an n-type semi-conductor is obtained. 

Metal alloys were first used in the Bronze Age (1,400 B.C.-O B.C.), where serendipity led to the discovery that doping copper with other compounds drastically altered the physical properties of the material. Artifacts from the Middle East dating back to 3,000 B.C. are found to consist of arsenic-doped copper, due to the wide availability of lautite and domeykite ores, which are rich in both arsenic and copper. However, due to arsenic-related casualties, these alloys were quickly replaced with tin-copper alloys (bronze) that were widely used due to a lower melting point, higher hardness, and lower brittleness relative to their arsenic forerunner. 

The small conductivity of silicon can be enhanced at normal temperatures if the silicon crystal is doped with certain other elements. For example, when a small fraction of silicon atoms is replaced by arsenic atoms, each having one more valence electron than silicon, extra electrons become available for conduction, as shown in Fig. 16.32(a). This produces an n-type semiconductor, a substance whose conductivity is increased by doping it with atoms having more valence electrons than the atoms in the host crystal. These extra electrons lie close in energy to the conduction bands and can easily be excited into these levels, where they can conduct an electric current [see Fig. 16.33(a)). 

Silicon s most familiar use is in the production of microprocessor chips. Computer microprocessor chips are made from thin slices, or wafers, of a pure silicon crystal. The wafers are doped with elements such as boron, phosphorus, and arsenic to confer semiconducting properties on the silicon. A photographic process places patterns for several chips onto one wafer. Gaseous compounds of metals are allowed to diffuse into the open spots in the pattern, and then the pattern is removed. This process is repeated several times to build up complex microdevices on the surface of the wafer. When the wafer is finished and tested, it is cut into individual chips. 

Silicon for semiconductor components must be doped with well-defined quantities of electron donors (phosphorus, arsenic or antimony) or electron donors (boron). This can be achieved by addition before pulling from a crucible, during zone melting (introduction of PH ) or by conversion of silicon into phosphorus by thermoneutron bombardment. 

Describe the nature of electrical conduction in (a) germanium doped with indium and (b) cadmium sulfide doped with arsenic. 

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