Semiconductor structure
LEDs are constructed using semiconductor materials, which are typically composed of layers of different materials.
The layers are carefully engineered to create a junction between different types of semiconductor materials: an N-type (negative) region and a P-type (positive) region. This junction is called a p-n junction.
Electron and hole movement
When a voltage is applied across the p-n junction of the LED, electrons from the N-type region are driven into the P-type region and positively charged "holes" from the P-type region are driven into the N-type region.
These electrons and holes are minority carriers in their respective regions and they combine at the p-n junction.
Recombination and light emission
When an electron from the N-type region recombines with a hole from the P-type region at the p-n junction, their energy levels are reduced.
This reduction in energy level results in the release of energy in the form of a photon (light particle). The energy of the photon determines the colour (wavelength) of the emitted light.
Direct bandgap materials
The specific semiconductor materials used in LEDs have a property known as a direct bandgap. This property enables efficient recombination of electrons and holes, leading to the emission of photons.
The bandgap energy determines the colour of light emitted. Different semiconductor materials and compositions are used to produce various colours of light, from red to blue and even ultraviolet.
Light extraction
The emitted photons are trapped within the semiconductor material due to total internal reflection. To extract the light and make it visible, LEDs are designed with surfaces that promote the escape of photons.
Reflective surfaces, textured surfaces, or encapsulation materials with specific refractive indices can help guide the light out of the LED chip.
Controlled colour and intensity
The colour and intensity of the emitted light can be controlled by adjusting the composition of the semiconductor materials and the current flowing through the LED.
By carefully engineering the materials and current levels, manufacturers can produce LEDs that emit a wide range of colours and brightness levels.
