An LED emits light by applying a forward current to the pn junction of a compound semiconductor.
Light-Emitting Diodes, or LEDs, are semiconductor devices that convert electrical energy directly into light. Unlike traditional incandescent bulbs that produce light through heat, LEDs use a process called electroluminescence.
The Mechanism of Light Emission in an LED
The fundamental principle behind an LED's operation involves the controlled movement and interaction of electrical charges within a specially designed material.
- Semiconductor Material: An LED is made from compound semiconductors. These materials have unique properties that allow them to emit light when electricity passes through them. Different compound semiconductors produce different colors of light.
- The PN Junction: Inside the LED is a pn junction. This is where a p-type semiconductor (with an excess of positive charge carriers called holes) meets an n-type semiconductor (with an excess of negative charge carriers called electrons).
- Applying Forward Current: Light emission occurs by applying a forward current to this pn junction. A forward current means that the positive terminal of a power source is connected to the p-type side, and the negative terminal is connected to the n-type side.
- Carrier Movement: When forward current is passed through the light-emitting diode, carriers (electrons and holes) move. Electrons from the n-type side are pushed towards the pn junction, and holes from the p-type side are also pushed towards the junction.
- Recombination: At the pn junction, electrons and holes meet. When an electron meets a hole, they recombine. In a compound semiconductor used for LEDs, this recombination process releases energy in the form of a photon – a particle of light.
- Light Emission: Billions of these recombinations happen every second when the LED is powered, resulting in the continuous emission of light that we see. The color of the light is determined by the energy difference between the electrons and holes in the specific compound semiconductor material used.
Key Factors in LED Operation
- Forward Bias: The LED must be connected in a specific direction (forward bias) for current to flow and light to be emitted. Connecting it in the reverse direction blocks current and prevents light emission.
- Current Control: The brightness of an LED is typically controlled by the amount of forward current flowing through it.
Understanding this process highlights why LEDs are significantly more energy-efficient than older lighting technologies; they directly convert electrical energy into light without the wasteful production of heat.
