Light-emitting diodes (LEDs) belong to the fourth (latest) generation of artificial light sources used by man in lighting so-called Solid State Lighting (SSL). The first 3 generations are: sources using the combustion process (I), incandescent lamps (II) and discharge lamps (III).

A light-emitting diode, also known as a light-emitting diode (LED), is one of the semiconductor optoelectronic devices that convert electrical energy into electromagnetic radiation energy. LEDs are usually produced as compounds of elements of groups III and V of the periodic table. In practice, both binary and multicomponent compounds are used, with the composition selected so that the semiconductor structure obtained in the technological process allows the emission of light in a given spectral range.

The least complex LEDs are realized in the form of ordinary semiconductor p-n junctions, which, polarized with a sufficiently large voltage in the direction of conduction, emit electromagnetic radiation in the visible and infrared light range. The wavelength of the radiation emitted by LEDs, and thus its color, depends on the semiconductor material from which it is made.

The operating principle of an LED is based on the phenomenon of electroluminescence, which involves the production of light under the influence of an electric field. Electroluminescence occurs as a result of recombination of holes and electrons in the p-n junction region. The transition of electrons from a higher energy level to a lower one is accompanied by the release of energy in the form of heat (non-radiative recombination) or light (radiative recombination). Non-radiative recombination occurs in semiconductors with an oblique energy gap, such as Si or Ge. Radiative recombination is characteristic of semiconductors with a straight energy gap. This type of recombination, during which energy is released in the form of radiation quanta - photons, occurs in materials such as GaAs, InAs, InP, InSb, for example.

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