What is the operating principle of a light-emitting diode?

Release Date:

2020-12-12

　　Light-emitting diodes are commonly used light-emitting devices that generate light through the recombination of electrons and holes. They are widely employed in the lighting industry. Light-emitting diode It can efficiently convert electrical energy into light and has a wide range of applications in modern society, such as lighting, flat-panel displays, and medical devices.

 

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　　This type of electronic component first appeared as early as 1962. In its early days, it could only emit low-intensity red light. Subsequently, other monochromatic versions were developed. Today, the range of emitted light has expanded to include visible, infrared, and ultraviolet wavelengths, and the luminous intensity has increased substantially. It is also used as indicator lights and display panels; with continuous technological advancements, light-emitting diodes have been widely adopted in displays and lighting applications.

　　Operating principle of light-emitting diodes:

　　Like a regular diode, Light-emitting diode It is composed of a p–n junction and also exhibits unidirectional conductivity. When a forward voltage is applied to the light-emitting diode, holes injected from the p-region into the n-region and electrons injected from the n-region into the p-region recombine with electrons in the n-region and holes in the p-region, respectively, within a few micrometers of the p–n junction. This recombination results in spontaneous radiative emission. The energy levels of electrons and holes vary depending on the semiconductor material; consequently, the amount of energy released during recombination differs. The greater the energy release, the shorter the wavelength of the emitted light. Commonly used LEDs emit red, green, or yellow light. The reverse breakdown voltage of an LED is greater than 5 volts, and its forward current–voltage characteristic curve is very steep, necessitating the series connection of a current-limiting resistor to control the current flowing through the diode.

　　The core of a light-emitting diode is a chip composed of P-type and N-type semiconductors. Between the P-type and N-type regions lies a transition layer known as the PN junction. In the PN junction of certain semiconductor materials, when minority carriers and majority carriers recombine, the excess energy is released in the form of light, thereby directly converting electrical energy into light energy. When a reverse voltage is applied across the PN junction, it becomes difficult for minority carriers to be injected, so no light is emitted. Under forward-bias conditions, as current flows from the LED’s anode to its cathode, the semiconductor chip emits light spanning various wavelengths—from ultraviolet to infrared. The intensity of the emitted light is proportional to the current.

 

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