VIAS Encyclopedia provides a collection of tables and definitions commonly needed in science and engineering.

Home Electronics Diodes Light-Emitting Diode
 
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Light-Emitting Diode

If a pn junction is operated in the forward direction, this will result in the recombination of the positive and negative charge carriers, whereby energy is released. With the conventional semiconductor materials (Si and Ge), this energy is released into the crystal in the form of heat. However, special semiconductor materials partially emit the released energy in the form of light. This light is practically monochromatic (typically 30 nm bandwidth), and the color of the light sent depends on the semiconductor material and its doping. Depending on the color, light-emitting diodes (light emitting diode = LED) are made out of GaAs, InAs, AlGaAs, GaP, GaAsP or GaN, and come in the colors blue, green, yellow, orange, red and infrared, respectively.

Semiconductor Wave Length (nm) Color
InAs 3480 infra red
GaAs 900 infra red
GaP + ZnO 690 red
GaAsP 660 red
AlGaAs 650 red
GaAsP + N 645 red
GaAsP 580 yellow
GaP + N 570 green
GaN 490 blue

When in use in the forward direction, they are switched to between 1 and 20 mA. With LEDs, particular attention should be given to the reverse voltage, since this is very low. Exceeding the reverse voltage will lead to the destruction of the element. LEDs are offered in different designs, as cylinders, prism and cubes. Seven segment displays contain seven LEDs which are arranged in form of the digit 8. In order to display a particular digit suitable segments are activated.
Left: typical form of a single LED; right: 7-segment display.
Home Electronics Diodes Light-Emitting Diode

Last Update: 2004-11-19