light-emitting diode

light-emitting diode:

see diode.

Light-emitting diode

A rectifying semiconductor device which converts electrical energy into electromagnetic radiation. The wavelength of the emitted radiation ranges from the near-ultraviolet to the near-infrared, that is, from about 400 to over 1500 nanometers.

Most commercial light-emitting diodes (LEDs), both visible and infrared, are fabricated from III–V semiconductors. These compounds contain elements such as gallium, indium, and aluminum from column III (or group 13) of the periodic table, as well as arsenic, phosphorus, and nitrogen from column V (or group 15) of the periodic table. There are also LED products made of II–VI (or group 12–16) semiconductors, for example ZnSe and related compounds. Taken together, these semiconductors possess the proper band-gap energies to produce radiation at all wavelengths of interest. Most of these compounds have direct band gaps and, as a consequence, are efficient in the conversion of electrical energy into radiation. With the addition of appropriate chemical impurities, called dopants, both III–V and II–VI compounds can be made p- or n-type, for the purpose of forming pn junctions. All modern-day LEDs contain pn junctions. Most of them also have heterostructures, in which the pn junctions are surrounded by semiconductor materials with larger band-gap energies. See Acceptor atom, Donor atom, Electroluminescence, Electron-hole recombination, Laser, Semiconductor, Semiconductor diode

Conventional low-power, visible LEDs are used as solid-state indicator lights in instrument panels, telephone dials, cameras, appliances, dashboards, and computer terminals, and as light sources for numeric and alphanumeric displays. Modern high-brightness, visible LED lamps are used in outdoor applications such as traffic signals, changeable message signs, large-area video displays, and automotive exterior lighting. General-purpose white lighting and multielement array printers are applications in which high-power visible LEDs may soon displace present-day technology. Infrared LEDs, when combined in a hybrid package with solid-state photodetectors, provide a unique electrically isolated optical interface in electronic circuits. Infrared LEDs are also used in optical-fiber communication systems as a low-cost, high-reliability alternative to semiconductor lasers.

Light-emitting diode

(LED)

1. Illumination technology that produces light by running electrical current through a semiconductor diode. LED lamps are much longer lasting and much more energy efficient than incandescent lamps; unlike fluorescent lamps, LED lamps do not contain mercury and can be readily dimmed.

2. Typically very low light output from a very tiny lamp. They are commonly used for decorative lighting and theater step lighting. Different semiconductors create different colors of light. LEDs are very long lasting; unlike fluorescent lamps, they do not contain mercury.

Light-Emitting Diode

 

(LED), a semiconductor device that converts electrical energy into the energy of optical radiation by making use of the phenomenon of injection electroluminescence in a semiconductor crystal with a p-n junction, a semiconductor heterojunction, or a metal-semiconductor contact. When a direct or alternating current flows in an LED into the semiconductor region adjacent to such a junction or contact,

Figure 1. Spectral transmission curves of several glass absorption filters that are 3 mm thick: (τ) transmission factor, (λ) wavelength of the light (1 nm = 10 Å). The wavelength range from 200 to 400 nm corresponds to near-ultraviolet radiation, the range from 400 to 700 nm corresponds to visible radiation, and the range from 700 to 1,200 nm corresponds to the near-infrared region of the spectrum.

excess charge carriers—electrons and holes—are injected; their recombination is accompanied by optical radiation.

LED’s emit radiation that is incoherent but has a narrower spectrum than that of thermal light sources. The radiation in the visible region is consequently perceived as monochromatic. The color of the radiation depends on the semiconductor material and its doping. Materials used in LED’s include compounds of the type A^IIIB^V and some other compounds; examples are GaP, GaAs, and SiC. Solid solutions are also used—for example, GaAs_l-xP_x, Al_xGa_l-xAs, and Ga_l-xIn_xP. Doping impurities used in GaP include Zn and O (red light) or N (green light); in GaAs there can be used Si or else Zn and Te (infrared light). The semiconductor crystal of an LED is usually given the shape of a wafer or hemisphere.

The luminance of the radiation of most LED’s is at the level of 10³ cd/m², and in the best models reaches 10⁵ cd/m². The efficiency of an LED producing visible radiation ranges from 0.01 percent to a few percent. In LED’s producing infrared radiation, the crystal is given a hemispherical shape to reduce losses resulting from total internal reflection and from absorption within the crystal. To improve the directivity characteristics of the radiation, LED’s are placed in a parabolic or conical reflector. The efficiency of an LED with a crystal of hemispherical shape reaches 40 percent.

Industry produces LED’s both as discrete devices and as components of integrated circuits. Discrete LED’s that produce visible light are used as signal indicators; integrated (multielement) LED devices—such as light-emitting digital display units, profile scales, multicolor panels, and flat screens—are used in various data display systems (seeDATA DISPLAY), in digital clocks, and in calculators. Infrared LED’s find application in, for example, optical-detection-and-ranging devices, optical-communications devices, and rangefinders (see alsoOPTICAL ELECTRONICS); arrays of such LED’s are used in data input and output devices for computers. In a number of areas of application, the LED competes with a related device—the injection laser (seeSEMICONDUCTOR LASER), which generates coherent radiation and differs from the LED in the shape of the crystal and in its manner of operation.

REFERENCE

Bergh, A., and P. Dean. “Svetodiody.” Tr. In-ta inzhenerov po eleklrotekhnike i radioelektronike, 1972, vol. 60, no. 2. (Translated from English.)

P. G. ELISEEV

light-emitting diode

[′līt i‚mid·iŋ ′dī‚ōd]

(electronics)

A rectifying semiconductor device which converts electrical energy into electromagnetic radiation. The wavelength of the emitted radiation ranges from the near-ultraviolet to the near-infrared, that is, from about 400 to over 1500 nanometers. Abbreviated LED.

Light-emitting diode

A rectifying semiconductor device which converts electrical energy into electromagnetic radiation. The wavelength of the emitted radiation ranges from the near-ultraviolet to the near-infrared, that is, from about 400 to over 1500 nanometers.

Most commercial light-emitting diodes (LEDs), both visible and infrared, are fabricated from III–V semiconductors. These compounds contain elements such as gallium, indium, and aluminum from column III (or group 13) of the periodic table, as well as arsenic, phosphorus, and nitrogen from column V (or group 15) of the periodic table. There are also LED products made of II–VI (or group 12–16) semiconductors, for example ZnSe and related compounds. Taken together, these semiconductors possess the proper band-gap energies to produce radiation at all wavelengths of interest. Most of these compounds have direct band gaps and, as a consequence, are efficient in the conversion of electrical energy into radiation. With the addition of appropriate chemical impurities, called dopants, both III–V and II–VI compounds can be made p- or n-type, for the purpose of forming pn junctions. All modern-day LEDs contain pn junctions. Most of them also have heterostructures, in which the pn junctions are surrounded by semiconductor materials with larger band-gap energies. See Laser, Semiconductor

Conventional low-power, visible LEDs are used as solid-state indicator lights in instrument panels, telephone dials, cameras, appliances, dashboards, and computer terminals, and as light sources for numeric and alphanumeric displays. Modern high-brightness, visible LED lamps are used in outdoor applications such as traffic signals, changeable message signs, large-area video displays, and automotive exterior lighting. General-purpose white lighting and multielement array printers are applications in which high-power visible LEDs may soon displace present-day technology. Infrared LEDs, when combined in a hybrid package with solid-state photodetectors, provide a unique electrically isolated optical interface in electronic circuits. Infrared LEDs are also used in optical-fiber communication systems as a low-cost, high-reliability alternative to semiconductor lasers.

light-emitting diode

A solid-state device (diode) that emits light of a single primary color, but in combination with other diodes can produce colors of any hue for use in signage. These devices, each of which is about one centimeter (half-inch), have a remarkably long life. Also called an LED.

light-emitting diode

(electronics)

(LED) a type of diode that emits light when current passes through it. Depending on the material used the colour can be visible or infrared. LEDs have many uses, visible LEDs are used as indicator lights on all sorts of electronic devices and in moving-message panels, while infrared LEDs are the heart of remote control devices.

See also smoke-emitting diode.