What are N-Type and P-Type Semiconductors?
12/11/2021 by MRL
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Semiconductors are commonly made of silicon because the material is easy to source and has an optimal electronic structure (its outer orbital has four electrons). Silicon can form beautiful and functional crystal structures, which, when merged to the four electrons, can form covalent bonds with neighbouring atoms, creating a lattice.
The problem is that this crystalline structure is a near insulator, so only tiny amounts of electricity can pass through it. Because silicone crystals are naturally intrinsic and used in almost every electronic device, they must be put through a doping process to increase the amount of electricity allowed to flow through them.
Doping refers to a chemical reaction that introduces impurities to a silicon crystal. These impurities allow the crystal’s atoms to form ionic bonds, making the once intrinsic crystal extrinsic. This process introduces two types of impurities; N-type and P-type. The ‘type’ it becomes depends on the materials used to create the chemical reaction.
The difference between N-type and P-type semiconductors is the primary material used to create the chemical reaction during doping. Depending on the material used, the outer orbital will have either five or three electrons making one negatively charged (N-type) and one positively charged (P-type).
Phosphorus or arsenic are the materials added to create an N-type semiconductor. These have five electrons in their outer orbital; the crystal has four. This means that one electron doesn’t have anything to bond with, so it moves around freely, increasing the flow of electrical current through the silicon.
P-type semiconductors have gallium or boron added as a catalyst, both of which only have three electrons in their outer orbitals. Adding these materials results in ‘holes’ being formed in the silicon atoms valence band, making the electrons mobile. The positively charged electrons move in the opposite direction of the holes.
While both result in better electrical conductivity, there still isn’t really enough to be as effective as they need to be until you put them together and create a diode. In its most basic form, an N-type has one too many electrons, and a P-type needs one more. Together, they give what the other needs and produces better electrical conductivity.
All in all, a computer chip is made up of billions of these diodes.
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