LEDs are versatile and can be found in various types in our daily lives. Common examples include through-hole LEDs and LED bulbs, which feature surface-mounted LEDs inside them.
What is an LED?
LED stands for Light-Emitting Diode, a semiconductor device that emits light when an electric current is applied. This process, known as electroluminescence, occurs when the movement of electrons within the semiconductor material generates photons, producing visible light.
Understanding Diodes
A diode is a two-terminal electronic component that allows current to flow in one direction. In a forward-biased state, the anode is positive, and the cathode is negative. When connected to a battery with the positive terminal to the anode and the negative terminal to the cathode, the diode allows current to flow easily.
In reverse bias, when the battery’s polarity is reversed, the diode blocks the current flow in the opposite direction. This behavior maintains the diode’s one-way functionality. Diodes are primarily made from semiconductor materials such as silicon or germanium.
Components and Structure of a Through-Hole LED
A through-hole LED consists of several components, including:
- Anode lead
- Cathode lead
- Reflective cup
- Semiconductor die
- Wire bond
- Lead frame
- Positive terminal
- Negative terminal
The main functional part of the LED is the semiconductor, which is divided into two regions: the P-type and N-type.
P-Type and N-Type Semiconductors
Silicon atoms have four valence electrons located in their outermost shell. These valence electrons form covalent bonds with neighboring silicon atoms, creating a crystal lattice structure. Each silicon atom contributes one electron to each of the four covalent bonds, resulting in no free electrons in pure silicon.
When a silicon atom is replaced with a boron atom, which has only three valence electrons, a deficiency of one electron arises in the lattice. This deficiency is referred to as a hole, and the resulting material is a P-type semiconductor, where positive charge carriers (holes) contribute to electrical conductivity.
Conversely, replacing a silicon atom with a phosphorus atom introduces an extra electron, creating a free electron in the crystal lattice. This results in an N-type semiconductor, where free electrons become the dominant charge carriers, contributing to electrical conductivity.
Formation of a PN Junction
When a P-type semiconductor is combined with an N-type semiconductor, a PN junction is formed at the interface where the two materials meet.
If the positive terminal of a voltage source is connected to the P-type material and the negative terminal to the N-type material, this forward biasingreduces the potential barrier at the junction. This allows charge carriers—holes from the P-type and electrons from the N-type—to move across the junction more easily. During this process, electrons recombine with holes, releasing energy in the form of light.
Conclusion
This mechanism of electron movement and recombination in the semiconductor material underpins the working principle of LEDs, making them efficient and versatile light sources for various applications.
