How LEDs work and a short guide on Semiconductors

Before explaining how Light Emitting Diodes (LEDs) work, let me give a quick introduction on semiconductor. Semiconductors are not good conductors of electricity due to very few free electrons (about 4-6 orders less free electrons than metals). This has to do with chemical bonding in the semiconductors, check this post. But, semiconductors can be manipulated by doping them with foreign elements to increase the number of free electrons. Let us take Silicon (Si) for example, Si has 4 covalent bonds with 4 adjacent Si atoms. If we dope Si with Phosphorous or Arsenic (P and As), we will end up with one extra free electrons as P or As can form 5 bonds. Similarly if we dope Si with either Boron or Alumnium (B and Al), we will end up with a free hole (absence of electrons, these can conduct electricity too) as B and Al can only form 3 bonds.



(Source of the image: LINK)

Doping is know as n-type if it results in an extra electron and p-type if an extra hole is created. An electron can combine with hole to release energy in a form of photon.

Now, let us come back to Light Emitting Diodes (LEDs). LEDs are made from combination of a p-type semiconductor and a n-type semiconductor. This combination is connected to a source of current (batttery or A/C power supply). Now when charge starts to flow in LEDs, one of the electron can combine with one of the hole to produce a photon (basically elementary particle of the light). And that's how LEDs work.


(Source of the image: LINK)

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