I'm in the process of learning how transistors works, which starts with understanding how doping is used to create n-type and p-type semiconductor materials.
All the resources I've read sort of explain this the same way, and I'm missing something. P-type semiconductors have extra holes and are predisposed to accept electrons, whereas n-type semiconductors have extra free electrons and are predisposed to donate them. This is the fundamental principle of how transistors work, as I understand it.
But every resource emphasizes that in spite of this both n-type and p-type semiconductors are electrically neutral, which is where I'm lost. If one has extra electrons, and one is missing electrons, how are they electrically neutral and not charged? I seem to have a block about this or something, I just don't get it.
Answer
Take silicon as an example. Silicon has four valence electrons, and silicon atoms in a crystal lattice form four bonds with neighbouring atoms.
Transistors, and other semiconductors, are made of silicon crystal with small amounts of dopants added. These dopants change the electrical properties because of the way they interact with the crystal lattice. Phosphorous, for example, has 5 valence electrons. It's still electrically neutral (number of protons = number of electrons) but since the silicon crystal structure only requires 4 bonds per atom, there is an 'extra' electron that isn't really participating in the crystal structure. With a bit of extra energy, that electron will go into the conduction band and freely roam around the crystal lattice. This corresponds to an n-type semiconductor.
There is a similar process for p-type semiconductors - boron, for example, only has 3 valence electrons.
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