On my quest to better understand how computers work at a deep level I have come to the question of why, exactly, silicon is used in microchips. I always assumed, naively, that silicon had a very high electrical resistance and so it made a good material to sandwich other materials with low electrical resistance (i.e. gold) in. And that this was the way that microchips were made.
After actually doing some research I see that I was wrong and that silicon is a 'semiconductor'. To keep this short I'll just skip forward and just say that I don't understand what a semiconductor is and why it's good for making microchips. I've seen several explanations and they either confused me, or the explanations completely contradicted each other, but the basic gist is that a semiconductor is somewhere in-between a conductor and an insulator. Why is that useful for making integrated circuits?
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Best Answer
Any of a number of semiconductor materials can be and are used, indeed the first transistor was actually a Germanium (Ge) transistor. the real reason why Si is so dominant comes down to 4 principal reasons ( but #1 is the primary reason):
1) It forms an oxide that is of very high high quality, seals the surface with very few pin holes or gaps. - this allows gap MOSFET to be more easily made as the SiO2 forms the insulating layer for the Gate, - SiO2 has been called the chip designers friend.
2) It forms a very tough Nitride, Si3N4 Silicon Nitride forms a very high bandgap insulator which is impermeable. - this is used to passivate (seal) the die. - this also used to make hard masks and in other process steps
3) Si has a very nice bandgap of ~ 1.12 eV, not too high so that room temperature can't ionize it, and not so low that it has to high leakage current.
4) it forms a very nice gate material. Most modern FET's used in VLSI (up until the latest generations) have been called MOSFET but in actual fact have used Si as the gate material. It turns out that it is very easy to deposited non-crystalline Si on surfaces and it is easily etched to great precision.
Basically the success of Si is the success of MOSFET, which with scaling and extreme integration has driven the industry. Mosfet's are not so easily manufactured in other material systems, and you can't drive the same level of integration in other semicondcutors.
GeO2 - is partially soluble
GaAs - does not form a oxide
CO2 - is a gas
Semiconductors are used because with selective contamination (called dopants) you can control the properties of the material and tailor it's operation and operational mechanisms.