The technology and the materials used are vital to understanding how the LED works.
Although the first PN junction had been in use for many years, it was not until 1962 that the LED was developed and its activity started to be understood worldwide.
LED technology: how a LED works
The semiconductor material used for the intersection must be a compound semiconductor. The commonly used semiconductor materials, including silicon and germanium, are simple elements and junction made from these materials does not emit light. Instead of compound semiconductors including gallium arsenide, gallium phosphide, and indium phosphide are compound semiconductors, and junctions made from these materials to emit light.
These compound semiconductors are classified by the valence bands their constituents occupy. For gallium arsenide, gallium has a valency of three and arsenic a valency of five and this is what is termed a group III-V semiconductor, and there are several other semiconductors that fit this category.
The light emitting diode emits light when it is forward biased. Holes from the p-type region and electrons from the n-type region enter the junction and recombine like a standard diode to enable the current to flow. When this occurs, energy is released, some of which is in the form of light photons.
It is found that the majority of the light is produced from the area of the junction nearer to the P-type region. As a result, the design of the diodes is made such that this area is kept as close to the surface of the device as possible to ensure that the minimum amount of light is absorbed in the structure.
To produce light which can be seen, the junction must be optimized and the correct materials must be 3chosen. Pure gallium arsenide releases energy in the infrared portion of the spectrum. Aluminum is added to the semiconductor to give aluminum gallium arsenide (AlGaAs) To bring the light emission into the visible red end of the spectrum.. Phosphorus can also be added to provide red light. For other colors, other materials are used. For example, gallium phosphide gives the green light, and aluminum indium gallium phosphide is used for yellow and orange light. Most LEDs are based on gallium semiconductors.