Schottky Barrier Diode


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Schottky barrier diode

[′shät·kē ¦bar·ē·ər ′dī‚ōd]
(electronics)
A semiconductor diode formed by contact between a semiconductor layer and a metal coating; it has a nonlinear rectifying characteristic; hot carriers (electrons for n-type material or holes for p-type material) are emitted from the Schottky barrier of the semiconductor and move to the metal coating that is the diode base; since majority carriers predominate, there is essentially no injection or storage of minority carriers to limit switching speeds. Also known as hot-carrier diode; Schottky diode.

Schottky Barrier Diode

 

(also Schottky diode), a semiconductor diode that is based on a metal-semiconductor contact. The Schottky barrier diode is named after W. Schottky, the German scientist who developed the principles of the theory of such diodes in 1938 and 1939.

Figure 1. The structure of a Schottky-barrier detector diode: (1) semiconductor substrate, (2) epitaxial film, (3) metal-semiconductor contact, (4) metal film, (5) terminal

Schottky barrier diodes are fabricated by depositing a thin film of metal—for example, Au, Al, Ag, or Pt—on the clean surface of a semiconductor crystal—such as Si, GaAs, or, less often, Ge—by means of vacuum evaporation, cathode sputtering, chemical deposition, or electrodeposition. In the contact region of the semiconductor, as in the junction region of a diode with a p-n junction, a potential barrier is formed (see alsoSCHOTTKY BARRIER). The variation of the height of the potential barrier when an external voltage, or bias, is applied results in a change in the current through the device (see, for example, Figure 2 in SEMICONDUCTOR DIODE). In contrast to the current through a p-n junction, the current through the metal-semiconductor contact is due only to majority carriers.

Figure 1. Energy diagrams for metal-semiconductor contacts: (a) a semiconductor and a metal before being brought into contact, (b) an ideal metal-n-type semiconductor contact, (c) an ideal metal-p-type semiconductor contact, (d) a real contact; (M) metal, (S) semiconductor, (D) dielectric layer, (SS) surface electronic states, (εvas) electron energy level in vacuum, (εv) electron energy level at the top of the valence band, (εc) electron energy level at the bottom of the conduction band, (εF) Fermi energy

Several features distinguish Schottky barrier diodes from other types of semiconductor diodes. A desired barrier height may be obtained by choosing an appropriate metal. The volt-ampere characteristic is substantially nonlinear at low forward biases. The time lag is very low, ranging down to 10–11 sec, and the highfrequency noise level is low. Schottky barrier diodes are technologically compatible with integrated circuits and are easy to fabricate.

Schottky barrier diodes are used mainly as microwave diodes for various applications, for example, as detector diodes (see Figure 1), mixer diodes, avalanche transit-time diodes, varactors, and multiplier diodes. In addition, they are employed as radiation detectors, nuclear radiation detectors, strain gages, and light modulators. They are also used in, for example, high-frequency current rectifiers and solar batteries.

REFERENCES

See references under SEMICONDUCTOR DIODE.

IU. R. NOSOV

Schottky barrier diode

A metal-semiconductor diode (two terminal electrical device) that exhibits a very nonlinear relation between voltage across it and current through it; formally known as a metallic disk rectifier. Original metallic disk rectifiers used selenium of copper oxide as the semiconductor coated on a metal disk. Today, the semiconductor is usually single-crystal silicon with two separate thin metal layers deposited on it to form electrical contacts. One of the two layers is made of a metal which forms a Schottky barrier to the silicon. The other forms a very low resistance, so-called ohmic, contact. The Schottky barrier is an electron or hole barrier caused by an electric dipole charge distribution associated with the contact potential difference which forms between a metal and a semiconductor under equilibrium conditions. The barrier is very abrupt at the surface of the metal because the charge is primarily on the surface. However, in the semiconductor, the charge is distributed over a small distance, and the potential gradually varies across this distance.

A basic useful feature of the Schottky diode is the fact that it can rectify an alternating current. Substantial current can pass through the diode in one direction but not in the other. If the semiconductor is n-type, electrons can easily pass from the semiconductor to the metal for one polarity of applied voltage, but are blocked from moving into the semiconductor from the metal by a potential barrier when the applied voltage is reversed. If the semiconductor is p-type, holes experience the same type of potential barrier but, since holes are positively charged, the polarities are reversed from the case of the n-type semiconductor. In both cases the applied voltage of one polarity (called forward bias) can reduce the potential barrier for charge carriers leaving the semiconductor, but for the other polarity (called reverse bias) it has no such effect. See Diode, Semiconductor, Semiconductor rectifier

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