How Light-Emitting Diodes (LEDs) Work

Light-Emitting Diode (LED) is a semiconductor device that directly converts electrical energy into light energy. Its operation primarily relies on the characteristics of the PN junction (Positive-Negative Junction) and semiconductor materials. Below is a detailed explanation of the basic working principle of LEDs.

Basic Structure of an LED

An LED primarily consists of P-type and N-type semiconductors. These two types of semiconductor materials form alternating layers to create the PN junction, which is the core component of the LED. In the P-type semiconductor, holes dominate; in the N-type semiconductor, electrons dominate.

How LEDs Work

When a forward voltage is applied to an LED (connecting the positive terminal to the positive lead and the negative terminal to the negative lead), electrons and holes begin to move, forming an electric current. At the interface of the PN junction, electrons flow from the N-type region to the P-type region, while holes flow from the P-type region to the N-type region. During this process, some electrons and holes “meet” at the interface and release energy in the form of photons. This is known as the “electroluminescence” phenomenon.

Energy Bands and Photon Emission

The light-emitting process of LEDs is closely related to their energy band structure. When electrons transition from a lower energy level to a higher one, they absorb energy. Conversely, when electrons return from a higher energy level to a lower one, they release energy in the form of photons. LEDs utilize this mechanism to convert electrical energy into light energy.

Current and Brightness

The brightness of an LED is directly proportional to the magnitude of the current flowing through it. Under forward voltage, as the current increases, the recombination rate of electrons and holes accelerates, leading to a greater number of emitted photons and enhanced brightness. However, to prolong the LED's lifespan, the current must be carefully controlled to prevent excessive heating and damage to the device.

Summary

The operating principle of light-emitting diodes (LEDs) is based on the electroluminescence phenomenon in semiconductor materials. By applying a forward voltage, electrons and holes recombine at the PN junction, releasing photons and converting electrical energy into light energy. LEDs offer advantages such as high efficiency, fast response times, long lifespan, energy savings, and environmental friendliness, making them widely used in lighting, displays, indicators, signaling, and other applications. With technological advancements, LED performance continues to improve, and their application areas are constantly expanding.