Principle of LED

The working principle of  light-emitting diodes

Light-emitting diodes, abbreviated as LEDs, are commonly used light-emitting devices that emit energy through the recombination of electrons and holes to emit light. They are widely used in the field of lighting.

Light-emitting diodes can efficiently convert electrical energy into light energy and have a wide range of uses in modern society, such as lighting, flat panel displays, and medical devices.

This kind of electronic component appeared as early as 1962. In the early days, it could only emit low-luminosity red light. Later, other monochromatic versions were developed. The light that can be emitted has spread to visible light, infrared and ultraviolet light, and the luminosity has also increased to a considerable luminosity. And the purpose is also as indicator light, display board, etc. from the beginning.

Light-emitting diodes are a special kind of diodes. Like ordinary diodes, light-emitting diodes are composed of semiconductor chips. These semiconductor materials will be injected or doped in advance to produce p and n structures.

Like other diodes, the current in light-emitting diodes can easily flow from the p-pole to the n-pole, but not in the opposite direction.

Two different types of carriers: holes and electrons flow from the electrode to the p, n structure under the action of different electrode voltages. When holes and electrons meet and recombine, the electrons will fall to a lower energy level, and at the same time they will release energy in the light mode.

The basic structure and circuit symbols of light-emitting diodes, principle analysis of light-emitting diodes

The color of the light emitted by the light-emitting diode is determined by the band gap energy of the semiconductor materials that make up the p and n structures.

Silicon and germanium are indirect band gap materials. At room temperature, the recombination of electrons and holes in these materials is a non-radiative transition. This type of transition does not release photons, but converts energy into heat, so silicon and germanium diodes cannot emit light.

The materials used in light-emitting diodes are all of the direct band gap type, and their energy is released in the form of photons. These band gap energies correspond to light energy in the near-infrared, visible, or near-ultraviolet bands.