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.