The device and principle of operation of LEDs. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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LEDs. The device and principle of operation of LEDs. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / LEDs

Light-emitting diode (abbreviated LED - light emitting diode, in the English version LED - light emitting duods) is a semiconductor device with an electron-hole pn junction or a metal-semiconductor contact that generates (when an electric current passes through it) optical (visible, UV, IR) radiation .

Recall that a pn junction is a "brick" of semiconductor electronic technology, representing two pieces of a semiconductor connected together with different types of conductivity (one with an excess of electrons - "n-type", the second with an excess of holes - "p-type"). If you apply a "forward bias" to the pn junction, that is, connect a source of electric current with a plus to the p-part, then current will flow through it.

We are interested in what happens after a current has flowed through a directly biased pn junction, namely moment of recombination (connection) of electric charge carriers - electrons and holes, when electrons having a negative charge "find a haven" in positively charged ions of the crystal lattice of a semiconductor. It turns out that such recombination can be radiative, while at the moment of the meeting of an electron and a hole, energy is released in the form of radiation of a light quantum - photon.

But not every pn junction emits light. Why? First, the band gap in the active region of the LED should be close to the energy of light quanta in the visible range. Second, the probability of emission during the recombination of electron-hole pairs must be high. To do this, the semiconductor crystal must contain few defects, due to which recombination occurs without radiation. These conditions contradict each other to some extent.

But in order to satisfy both conditions, one pn junction in the crystal is not enough. It is necessary to manufacture multilayer semiconductor structures, the so-called heterostructures. For the study of these structures, the Russian physicist Zhores Zh. I. Alferov (academician, director of the A. F. Ioffe Physical-Technical Institute, laureate of the Lenin Prize) received the gold medal of the American Physical Society for studies of heterostructures based on Ga_1-xAl_xAs back in the 70s.

In 2000, when it became clear how important these works are for the development of science and technology, how important their practical applications are for mankind, he was awarded the Nobel Prize.

Author: Koryakin-Chernyak S.L.

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