How are light emitting diodes made?

Answer 1

They are made exactly the same way as ordinary semiconductor diodes, except that "binary semiconductors" (i.e. semiconductors made of two or more elements) are used instead of the silicon or germanium that ordinary diodes are made of.

First these "binary semiconductors" have a much wider bandgap than silicon does, causing a photon to be generated by each electron dropping into a hole at the device junction.

Second that "binary semiconductors" are selected to be transparent to the generated photons, allowing them to escape (both silicon and germanium are opaque to photons).

By selecting different elements to make the "binary semiconductors" for the light emitting diodes, different width bandgaps can be produced causing photons of different energy (i.e. color) to be generated. A narrow bandgap produces infrared, a slightly wider bandgap produces red light, and so on up the rainbow until very wide bandgaps produce blue light or even ultraviolet. An ultraviolet light emitting diode can be coated with a phosphor (like a fluorescent light is) to produce white light.