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Introduction
Published in J. R. Coaton, A. M. Marsden, Lamps and Lighting, 2012
The requirements for an LED of a pure single crystal material which can be doped both p-type and n-type are satisfied by many of the semiconductor III–V compounds. Some of the most important commercially available LEDs are based on gallium arsenide and gallium phosphide. The former ha? a direct band gap of 1.49 eV and is an efficient infrared electroluminescent emitter. Gallium phosphide has an indirect gap of 2.25 eV. They form a continuous solid solution over the entire arsenic-phosphorus range: the alloy gallium arsenide phosphide (GaAsP) can be tailored by adjusting the arsenic/phosphorus ratio to give intermediate band gaps and LEDs that emit the colours red, orange and yellow. Other alloys have been developed for high brightness red LEDs based on AlGaAs heterostructures where the p and n parts of the junction are made from different AlGaAs compositions. Gallium phosphide can be doped to give red and green LEDs, and gallium nitride and silicon carbide can be used to produce blue.
Display Devices
Published in John C. Morris, Digital Electronics, 2013
Light emitting diodes are constructed from a pn junction just like a normal silicon diode. Different semiconductor materials are employed in the fabrication process, usually Gallium Phosphide (GaP) or Gallium Arsenide Phosphide (GaAsP). Into this material some impurity is added, it is this together with the base semiconductor that will determine the wavelength and hence the colour of the emitted light.
UK Team to be world leaders in studying the recovery of gallium from WEEE
Published in Transactions of the IMF, 2021
LEDs have been known for over a century and the first one was a crystal of silicon carbide (SiC), but it was not until the early 1960s that a visible light LED was developed. These LEDs use materials including gallium arsenide (GaAs), gallium phosphide (GaP) and gallium arsenide phosphide (GaAsP) to make the light-producing process more efficient. LEDs also have carefully controlled amounts of indium or aluminium added, and they can also be doped with other elements such as magnesium. These dopants result in the generation of coloured LEDs – notably red, orange, yellow and green. LEDs emitting blue light are based on silicon carbide and gallium nitride. The colour and intensity of an LED depends on the combination of materials used and the energy gaps of the positive (p) and negative (n) materials used in the diode. An important part of the project will be to separate out these dopant metals to ensure a high purity output of metallic gallium.