LEDs have been in use for many years, they are a two-lead semiconductor lighting source, a junction diode that emits light when activated.

We are all used to seeing LEDs on the front of electrical devices showing either an on or off state, it does this when a suitable voltage is applied, electrons are then able to recombine with electron holes within the device then releasing energy in the form of protons creating electroluminescence, this light, this can be of visible or invisible light (to the human eyes).

LEDs are used for many diverse applications including residential and commercial lights, aviation lighting as well as advertising boards, traffic signals, lighted wallpaper and appliances and medical devices. They have become very popular due to their low production and purchase cost as well as for their low energy cost running and overall longevity.


Developments of the Light emitting diode

The first experimental LED was discovered in 1907 by H.J. Round when using some silicon carbide and a cats whisker combining them with electricity to create light.

James R. Biard and Garry Pittman developed the infrared LED at Texas instruments in 1961, it was the first modern LED and was discovered purely by accident when an X-band GaAs varactor diode was being made, a reaction between the zinc diffused area was observed across the GaAs (Gallium Arsenide) semi-insulating surface.

The next year, in 1962, Nick Holonyack (At General Electric) develops the red LED, this was the first semiconductor source with visible light, he uses a Gallium Arsenide Phosphide on a GaAs substrate.

It took another 10 years until M. George Craford (of St Louis, Missouri) creates the first yellow LED at Monsanto using GaAsP, he also developed a brighter red LED.

In the same year, Herbert Maruska and Jacques Pankove (RCA labs, New Jersey)  developed the violet ED using Mq-doped GaN films. The violet LED was the foundation for the true blue LED that was developed later.

In 1979, Shuji Nakamura (Tokushima, Japan) develops the world very first blue LED, it was a bright source using Gallium Nitride but would take more than 20 years until the blue LED would become of a low cost with the manufacturer for mass commercial production.

Organic compounds

LEDs are manufactured by a process of sandwiching organic compounds between a silicon substrate – when energy is applied, molecules reform through a gate to produce light, the energy only works one way in one polarity.

Different organic compounds create different coloured light:

Wavelength Colour Material
< 400 ultraviolet Aluminium nitride (AIN)
Aluminium gallium nitride (AIGan)
Aluminium gallium nitride (AlGaN)
400 – 450 violet Indium gallium nitride (InGaN)
450 – 500 blue Indium gallium nitride (InGaN)
Silicon carbide (SiC)
500 – 570 green Gallium phosphide (GaP)
Aluminium gallium indium phosphide (AlGaInP)
Aluminium gallium phosphide (AlGaP)
570 – 590 yellow Gallium arsenide phosphide (GaAsP)
Aluminium gallium indium phosphide (AlGaInP)
Gallium phosphide (GaP)
590 – 610 orange/amber Gallium arsenide phosphide (GaAsP)
Aluminium gallium indium phosphide (AlGaUInP)
Gallium phosphide (GaP)
610-760 red Aluminium gallium arsenide (AlGaAs)
Gallium arsenide phosphide (GaAsP)
Aluminium gallium indium phosphide (AlGaInP)
Gallium phosphide (GaP)
>760 infrared Gallium arsenide (GaAs)
Aluminium gallium arsenide (AlGaAs)

 

OLED devices like televisions and mobile phones as well as smart devices have many LEDs packed together tightly into arrays and can be switched on and off very quickly to produce a picture that we can see.

It just goes to show that there are many organic compounds around us working seamlessly with integrated circuits and electronics and it all started from a cats whisker!