Doping, semiconductors

The electrical conductivity of a semiconductor is influenced by the presence of small numbers of impurity atoms. The process of adding controlled amounts of impurity atoms to a material is known as doping. Consider what happens when a few phosphorus atoms (known as dopants) replace silicon atoms in a silicon crystal. In pure Si all of the valence-band molecular orbitals are filled and all of the conduction-band molecular orbitals are empty, as T FIGURE 12.32(a) shows. Because phosphorus has five valence electrons but 

The dramatic change in conductivity in response to the addition of a trace amount of a dopant means that extreme care must be taken to control the impurities in semiconductors. It also provides an opportunity for controlling the electrical conductivity through precise control of the type and concentration of dopants. 

The junction of an n-type semiconductor with a p-type semiconductor forms the basis for diodes, transistors, solar cells, and other devices. 

Which of the following elements, if doped into silicon, would yield an n-type semiconductor  

Analyze An n-type semiconductor means that the dopant atoms must have more valence electrons than the host material. Silicon is the host material in this case. 

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It is used as a fluorinating reagent in semiconductor doping, to synthesi2e some hexafluoroarsenate compounds, and in the manufacture of graphite intercalated compounds (10) (see Semiconductors). AsF has been used to achieve >8% total area simulated air-mass 1 power conversion efficiencies in Si p-n junction solar cells (11) (see Solarenergy). It is commercially produced, but usage is estimated to be less than 100 kg/yr. 

Although there has been theoretical and experimental interest in the effects of ion bombardment on materials since about 1960 (153), the growth in ion implantation technology and appHcations since then is due almost solely to the semiconductor (integrated circuit) industry. The advantages of ion implantation for semiconductor doping were first pointed out in 1955 (154), but these advantages were not widely accepted until about 1970. 

Semiconductor doping, n or p Metal system Contact type" Anneal temp, °C Typical Reference... 

Boron Bromide. Approximately 30% of BBr produced in the United States is consumed in the manufacture of proprietory pharmaceuticals (qv) (7). BBr is used in the manufacture of isotopicaHy enriched crystalline boron, as a Etiedel-Crafts catalyst in various polymerization, alkylation, and acylation reactions, and in semiconductor doping and etching. Examples of use of BBr as a catalyst include copolymerization of butadiene with olefins (112) polymerization of ethylene and propylene (113), and A/-vinylcarbazole (114) in hydroboration reactions and in tritium labeling of steroids and aryl rings (5). 

Materials made of siHcon nitride, siHcon oxynitride, or sialon-bonded siHcon carbide have high thermal shock and corrosion resistance and may be used for pump parts, acid spray nozzles, and in aluminum reduction ceUs (156—159). A very porous siHcon carbide foam has been considered for surface combustion burner plates and filter media. It can also be used as a substrate carrying materials such as boron nitride as planar diffusion source for semiconductor doping appHcations. 

Implantation dose or fluence it controls the amount of dopant (i.e., its local concentration) introduced in the target per unit surface area. It is measured in ions/cm and it is the integral over the depth of the concentration profile. Typical values in the nanocluster synthesis are lO -lO ions/cm. For a comparison, the t5 pical fluence values for semiconductor doping processes are 10 -10 ions/cm. ... 

Calvet and Guillaud (S3) noted in 1965 that in order to increase the sensitivity of a heat-flow microcalorimeter, thermoelectric elements with a high factor of merit must be used. (The factor of merit / is defined by the relation / = e2/pc, where e is the thermoelectric power of the element, p its electrical resistivity, and c its thermal conductivity.) They remarked that the factor of merit of thermoelements constructed with semiconductors (doped bismuth tellurides usually) is approximately 19 times greater than the factor of merit of chromel-to-constantan thermocouples. They described a Calvet-type microcalorimeter in which 195 semiconducting thermoelements were used instead of the usual thermoelectric pile. 

Semiconductor device manufacture, high purity oxygen in, 13 459 Semiconductor doping, in ion implantation, 14 446-447... 

Semiconductors doped Band gap (uV) Sacrificial reagent Rate of gas evolution (fimol/h) Ref... 

For the case of semiconductors doped with donors ( -type) and acceptors (p-type), three regions can be distinguished. In the low-temperature extrinsic region kT Eg), the conductivity is given by... 

The question of n- and p-type (excess charge carriers in conductivity and valence band, respectively) mechanisms of semiconductors is shown in Figs. 7.28 and 7.29. For this reason, p-type electrodes will be suitable as anodes,23 i.e., a deelectronation reaction, in which electrons are accepted from ions in the solution layer next to the electrode into the waiting holes in the valence band. Semiconductor doped n will be cathodes. 

In practice, this limitation is not seriously restrictive. Moderate electrolyte concentrations (t 0.5N) are required by solution IR drop concerns, yielding ds on the order of a few angstroms. Optimal semiconductor doping levels are dictated by developing H with the approximate value of a l, where a is the semiconductor absorption coefficient, and H is the depletion width. As a consequence, a typical order of magnitude for H is 1 micron (104 A). Thus the ratio H/ds... 

Zeolites provide a novel host for the generation of semiconductor hyperlattices within their pore volume. The control of the connectivity between the clusters of semiconductor is unparalleled in any other host medium and so has allowed a detailed study of the optical consequences of such connectivity6. However, from the practical standpoint, such materials have some severe drawbacks - most notably the lack of single crystals of sufficient size to produce viable optical devices such as optical transistors or spatial light modulators. We have therefore moved on to look at more practical/processable quantum-dot materials such as semiconductor-doped porous glasses. 

If, on the other hand, the field forces the mobile holes away from the surface, a space charge region consisting of the ionized acceptor atoms, which are fixed in the lattice, forms over an appreciable distance into the semiconductor. The thickness of the surface space charge region is a function of the strength of the field at the surface and the semiconductor doping profile, as is the difference between the surface potential and the bulk potential of the semiconductor. If the surface potential deviates sufficiently far from the bulk potential, the surface will invert that is, it will contain an excess of mobile electrons. In this case, an -type conductive channel... 

In the case of semiconductors doped with f elements a different kind of an energy transfer process can be observed, namely from extended band states or excitonic states to the highly localized f-element states. Such a process is different from the cases discussed in the preceding sections, where the energy transfer from point defects (or at the most molecular states) was considered. The interest in semiconductors doped with f elements is obvious, because of their potential to combine sharp f-element luminescence with the possibility of simple electrical excitation via the semiconductor host. However, a quenching of the luminescence with... 

Semiconductors are materials with electrical conducting properties somewhere between those of insulators and conductors. p-Type semiconductors are semiconductors doped with an element having fewer valence electrons than silicon or germanium. n-Type semiconductors are semiconductors doped with an element having more valence electrons than silicon or germanium. 

Typical values of the second-order nonlinear coefficient d for dielectric crystals, semiconductors, and organic materials used in photonics applications lie in the range d = 10 24 to 10 - (mks units, As/V2). Typical values of the third-order nonlinear coefficient x(3> for glasses, crystals, semiconductors, semiconductor-doped glasses, and organic materials of interest in photonics are x -3 = 10 34 to 10 29 (mks units). 

Kokorin, Alexander I, was bom in 1947. Was graduated as a biophysicist in 1970 Ph.D. (Candidate of Sciences) in 1974 D.Sc. degree (Doctor of Sciences) in physical chemistry - in 1992. At present Principal Researcher and Deputy Head of the Division of Kinetics and Catalysis, N. Semenov Institute of Chemical Physics of Russian Academy of Sciences, Moscow, Russia. Area of research interests chemical methods of solar energy conversion chemical physics of organized molecular systems, including nanosized oxide semiconductors doped with transition metal ions, and polymer-metal complexes the study of their structure, absorptive, catalytic, photocatalytic and photoelectrochemical properties. EPR spectroscopy and spin-spin interaction between paramagnetics. He is the author and co-author of more than 170 publications, including two books and several reviews and book chapters. 

The most investigated crystals from the polariton point of view are ionic crystals, studied by IR spectroscopy.156 (Other applications of polariton theory are time spectroscopy and nonlinear optics in semiconductors182 and semiconductor-doped glasses.183) The mixed crystals are of the type K(C1, Br)... 

Semiconductor Doping Solid-State Diffusion Ion Implantation... 

The signal travels through a thick, or even molecularly thin, semiconductor that connects these electrodes it could be an inorganic semiconductor (doped Si, doped Ge), an organic conducting polymer (polyaniline, polythiophene, polyacetylene), a carbon nanotube, or an organic semiconductor (sexithiophene). 

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