Optical diodes ( light emitting diodes emit light )

hi,first of all sorry for grammar because my first language is not english

first question: I know that diodes are made of two positive and negative semiconductors What exactly causes ordinary diodes not to emit light, but light emitting diodes emit light?Although both are made of PN Junction.Please give an accurate and correct answer.

second question: Are light emitting diodes made of silicon? like rectifier diodes?Please answer second question with yes or no. thanks a lot

by RezaJ1992
July 07, 2020

When a moving electron recombine into a "hole", the energy can be released as a photon which frequency has to match the energy gap. With standard impurities, that does not correspond to a visible light. We can change the impurities or the substrate to match a desirable wavelength and/or add phosphorus to capture then reemit visible light (like phosphorus light). Most LED can't hold a strong voltage in reverse and thus, have very little use as diode. They have to be made of a material transparent to the magnetic wave length that is desirable, while standard diode and integrated circuit are encapsulated in opaque material to avoid outside interference.

by vanderghast
July 08, 2020

I found that the core of the diodes and the LEDs are the same, but the coating material of the LEDs is clear and the coating material of the diodes is opaque.Is this true?

by RezaJ1992
July 10, 2020

please just say me with yes or no or with shape because my first language is not english And I hardly understand thanks a lot.

by RezaJ1992
July 10, 2020

No. As example, blue LED are made of some GaN (over a substrate of silicon, but that substrate is used to grow the GaN crystal).

by vanderghast
July 10, 2020

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