Transistor doped

The bipolar junction transistor (BIT) consists of tliree layers doped n-p-n or p-n-p tliat constitute tire emitter, base and collector, respectively. This stmcture can be considered as two back-to-back p-n junctions. Under nonnal operation, tire emitter-base junction is forward biased to inject minority carriers into tire base region. For example, tire n type emitter injects electrons into a p type base. The electrons in tire base, now minority carriers, diffuse tlirough tire base layer. The base-collector junction is reverse biased and its electric field sweeps tire carriers diffusing tlirough tlie base into tlie collector. The BIT operates by transport of minority carriers, but botli electrons and holes contribute to tlie overall current. 

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. 

Gallium wets glass or porcelain and forms a brilliant mirror when it is painted on glass. It is widely used in doping semiconductors and producing solid-state devices such as transistors. 

DCFET. See Doped channel field-effect transistor. 

MODFET. See Modulation doped field-effect transistor. 

Autodopiag occurs whea dopants are unintentionally released from a substrate through diffusion and evaporation, and subsequently reiacorporated during the deposition layer. Epitaxial layers are typically doped at concentrations of lO " -10 atoms/cm. The higher levels of doping are used in bipolar technology where the epilayer forms the transistor base. The epitaxial layer can be up to several hundred micrometers, and as thin as 0.05—0.5 p.m. Uniformities of 5% are common. 

Fig. 5. Bipolar transistor (a) schematic and (b) doping profiles of A, arsenic ion implanted into the silicon of the emitter ( -type) B, boron ion implanted into the silicon of the base (p-type) C, antimony ion implanted into the buried layer ( -type) and D, the epi layer...

To achieve the lowest possible delay a bipolar switching transistor developed by IBM minimizes parasitic resistances and capacitances. It consists of self-aligned emitter and base contacts, a thin intrinsic base with an optimized collector doping profile, and deep-trench isolation (36). Devices must be isolated from each other to prevent unwanted interactions in integrated circuits. While p—n junctions can be used for isolation, IBM s approach etches deep trenches in the siUcon wafer which are filled with Si02 to provide electrical insulation. 

In an HBT the charge carriers from an emitter layer are transported across a thin base layer and coUected by a third layer called the coUector. A small base current is present which iacludes the carriers that did not successfully cross the base layer from the emitter to the coUector. The FET is a unipolar device making use of a single charge carrier in each device, either electrons or holes. The HBT is a bipolar device, using both electrons and holes in each device. The emitter and coUector layers are doped the same polarity n- or -type), with the base being the opposite polarity (p- or n-ty- e). An HBT with a n-ty e emitter is referred to as a n—p—n device ap—n—p device has a -type emitter. The n—p—n transistors are typicaUy faster and have been the focus of more research. For the sake of simplicity, the foUowing discussion wiU focus on n—p—n transistors. 

Germanium (pure), galium arsenide Germanium (doped, transistor-grade)... 

Contacts are the elementary building blocks for all electronic devices. These include interfaces between semiconductors of different doping type (homojunctions) or of different composition (heterojunctions), and junctions between a metal and a semiconductor, which can be either rectifying (Schotlky junction) or ohmic. Because of their primary importance, the physics of semiconductor junctions is largely dealt with in numerous textbooks [11, 12]. We shall concentrate here on basic aspects of the metal-semiconductor (MS) and, above all, metal-insulator-semiconductor (MIS) junctions, which arc involved in the oiganic field-effect transistors. 

Silicon can be doped with small amounts of phosphorus to create a semiconductor used in transistors, (a) Is the alloy interstitial or substitutional Justify your answer, (b) How do you expect the properties of the doped material to differ from those of pure silicon ... 

The start of the solid-state electronic industry is generally recognized as 1947 when Bardeen, Brattain, and Shockley of Bell Telephone Laboratories demonstrated the transistor function with alloyed germanium. The first silicon transistor was introduced in 1954 by Texas Instruments and, in 1956, Bell Laboratories produced the first diffused junction obtained by doping. The first-solid state transistor diodes and resistors had a single electrical function and were (and still are) known as discrete devices. 

A photovoltaic cell is basically a semiconductor diode consisting of a junction similar to the junction of a transistor. An electrical potential is formed by n-type doping on one side and p-type on the other. Under the impact of light (photons), such as in sunlight, electrons move from the p side, across the junction to the n side, and, through electrical contacts, can be drawn as a usable current (Fig. 15.4). 

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 TFTs are made on transparent glass substrates, onto which gate electrodes are patterned. Typically, the gate electrode is made of chromium. This substrate is introduced in a PECVD reactor, in which silane and ammonia are used for plasma deposition of SiN as the gate material. After subsequent deposition of the a-Si H active layer and the heavily doped n-type a-Si H for the contacts, the devices are taken out of the reactor. Cr contacts are evaporated on top of the structure. The transistor channel is then defined by etching away the top metal and n-type a-Si H. Special care must be taken in that the etchant used for the n-type a-Si H also etches the intrinsic a-Si H. Finally the top passivation SiN, is deposited in a separate run. This passivation layer is needed to protect the TFT during additional processing steps. 

The silver(I) complexes with the tetrakis(methylthio)tetrathiafulvalene ligand have been reported, the nitrate salt presents a 3D structure with an unprecedented 4.16-net porous inorganic layer of silver nitrate,1160 the triflate salt presents a two interwoven polymeric chain structure.1161 The latter behaves as a semiconductor when doped with iodine. With a similar ligand, 2,5-bis-(5,5,-bis(methylthio)-l,3,-dithiol-2 -ylidene)-l,3,4,6-tetrathiapentalene, a 3D supramolecular network is constructed via coordination bonds and S"-S contacts. The iodine-doped compound is highly conductive.1162 (Methylthio)methyl-substituted calix[4]arenes have been used as silver-selective chemically modified field effect transistors and as potential extractants for Ag1.1163,1164... 

H. Morkoc and H. Vnlu, Factors Affecting the Performance of (Al, Ga)As/GaAs and (Al, Ga)As/InGaAs Modulation-Doped Field-Effect Transistors Microwave and Digital Applications... 

See also Field effect transistors (FETs) Doped oxide semiconductor coatings, 23 17-19... 

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