Conductor-semiconductor diode

Since both metals and degenerate semiconductors have been used as the counter-electrode to the semiconductor in both diode and capacitor-type devices, a more general notation than that usually found in the literature will be employed in this review. This more generalized notation will refer to the counter-electrode as the conductor (c). Hence, M-S, M-I-S, and degenerate semiconductor-interfacial layer-semiconductor diode devices all become C-S or C-I-S... 

A substrate 10 of HgCdTe is provided with an upper surface region 11 formed by an annealing procedure, or as an epitaxial layer or evaporated film. A layer of insulating material 12 is formed in which windows are provided. The windows are partially filled with a thin layer of metal 13 which is deposited therein to form a metal-semiconductor diode with the upper surface region. The metal layer is deposited to a thickness on the order of 10-50 nm thick and is sufficiently thin to be semi-transparent to infrared radiation. A thick layer of metal 14 is deposited to form an expanded contact and an anti-reflection coating 15 is provided. External conductors in the form of jumper wires 16 are ball bonded to the contact 14. 

Using these two methods nanoscale circuits, consisting of conductors, semiconductors and isolating areas, can be obtained. Elements such as tunnel resonant diodes and single electron transistors can be the structural elements of such circuits, analogous to devices described in the literature [50]. 

Thin films (qv) of vitreous silica have been used extensively in semiconductor technology. These serve as insulating layers between conductor stripes and a semiconductor surface in integrated circuits, and as a surface passivation material in planar diodes, transistors, and injection lasers. They are also used for diffusion masking, as etchant surfaces, and for encapsulation and protection of completed electronic devices. Thin films serve an important function in multilayer conductor insulation technology where a variety of conducting paths are deposited in overlay patterns and insulating layers are required for separation. 

The mechanisms of detection and the functions of the conductor layer and of the semiconductor are the same in a C-I-S diode sensor as they are in a C-S diode sensor. The only difference between these two structures is the presence of the purposefully inserted interfacial layer (I-layer) between the conductor and the semiconductor in the C-I-S devices. In general, this I-layer is employed in the C-I-S sensor configuration for one of two reasons (1) either it is used to block chemical reactions between the conductor and the semiconductor or (2) it is used to augment or reduce the role of the interface in establishing the double layer or controlling transport. 

If a conductor material undergoes a work function change when exposed to a certain chemical species, then clearly one has the foundations of a C-S diode sensor. However, this sensor cannot be made to function if the conductor chemically reacts with the semiconductor. This loss of sensitivity occurs because the new material resulting from the reaction, in general, will not have the same work function sensitivity to the chemical species as the conductor has. The C-I-S configuration solves this problem since a properly chosen I-layer, capable of supporting an electrical current, can be inserted between the conductor and semiconductor to prevent their reaction. The resultant C-I-S structure is able to respond to the effects of the gas species on the conductor. 

Asymmetric conductors have isymmetric I — V curves. This phenomenon is known as the diode or ratchet effect and plays a major role in electronics. Recently much interest has been attracted by transport asymmetries in singlemolecule devices and other mesoscopic systems [1], The idea that asymmetric molecules can be used as rectifiers is rather old [2], however, it was implemented experimentally [3] only recently. Another experimental realization of a mesoscopic rectifier is an asymmetric electron waveguide constructed within the inversion layer of a semiconductor heterostructure [4]. The ratchet effect was observed in carbon nanotubes [5], and strongly asymmetric I — V curves were recently reported for the tunneling in the quantum Hall edge states [6]. These experimental advances have stimulated much theoretical activity [7, 8, 9, 10, 11] with the main focus on the simplest Fermi-liquid systems [12]. 

In electronics, a well-established procedure to make statements on the sign of the electronic carriers is establishing the appropriate junctions (cf. diodes). The transformability of the semiconductor experiments to ion conductors suffers from the fact that the situation in ion conductors is more related to the situation in relaxation type semiconductors than to lifetime semiconductors note that only the latter shows the typical significant electronic effects such as in diodes or transistors. Nonetheless setting up ionic diodes and ionic transistors may be a worthwhile task for the future. (One such attempt to find out the nature of the ionic carriers (Oj or Vq ) in PbO by diode effects, viz. by a contact to the vacancy conductive YSZ, has been reported in Ref.217)... 

Al, Ga and In form tetrahedrally coordinated solids with elements of group 15, which are part of the series of III-V semi-conductor (i.e., groups 13-15). The mixed compounds gallium aluminium phosphides Ga r AljP and the arsenide Gaj r AljAs are used for light-emitting diode (LED) displays and semiconductor lasers. 

This notation, where n-type refers to an electron conductor, and retype refers to a hole (lack of electron) conductor, indicates how a semiconductor was processed. For example, a p-type semiconductor material layer grown on an n-type substrate forms a (p — n) diode, which can be used to rectify alternating current. A p — n — p device may be used as a transistor, and is useful as a signal amplifier or for other applications. 

As mentioned earlier, photochemical diodes489 can be either of the Schottky type, involving a metal and a semiconductor, or a p n junction type, involving two semi conductors (which can be the same, i.e., a homojunction or different, a heterojunc tion). Only the latter type is considered in this Section involving two irradiated semi conductor/ electrolyte interfaces. Thus n Ti02 and p-GaP crystal wafers were bonded together (through the rear Ohmic contacts) with conductive Ag epoxy cement.489 The resultant heterotype p n photochemical diode was suspended in an acidic aqueous... 

An important area where technology and heterocyclic chemistry combine is that of electroactive organic materials. The applications of these materials, which extend beyond simple replacements for metals, include use as conductors, superconductors, semiconductors, batteries, transistors, sensors, light emitting diodes (LEDs), and related electrochromic applications. This area is of great commercial importance. 

Semiconductor rectifiers contain at least two separate materials, a P-type and an N-type silicon semiconductor, joined together and held by conductors. With an alternating voltage across this combination, normally called a silicon diode, the electrons in the N-layer and the holes in the P-layer respond by moving in opposite directions. Figure 8.6 shows that during one half of the voltage cycle, the electrons and holes move toward the junction, and current flows. In the other half of the cycle, the electrons and holes move away from the junction, and current flow is impossible. 

Unfortunately, the term semiconductor refers not just to half-good conductors, which might be confusing. Semiconductors most often refers to those materials that are the basis for devices that are steerable in a certain fashion such as diodes, transistors, etc. ie, the basics for computers. We leave the details aside. 

An LED is a specific type of solid-state diode, but it stiU retains the other properties typical of diodes. Solid-state diodes are formed at the junction of two semiconductors of different properties. Semiconductors are materials that are inherently neither good conductors nor good insulators. The electrical properties of the materials making up semiconductors can be altered by the addition of impurities into the crystal structure of the material as it is fabricated. Adding impurities to semiconductors to achieve the proper electrical nature is called doping. If the added impurity has one more electron in its outermost electron shell compared with the semiconductor material, then extra electrons are available to conduct electricity. This is a negative doped, or n-type, semiconductor. However, if the impurity has one fewer electron in its outermost electron shell compared with the semiconductor material, then there are too few electrons in the crystal structure, and an electron... 

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