Semiconductor Doping

WOAH WOAH WOAH SLOW DOWN. WHAT EVEN ARE SEMICONDUCTORS?

They’re the materials that transistors are made from. Transistor are the little guys that power your phone and laptop, and sent man to the moon.

If you read my previous post you’ll know the interesting story of how semiconductors came about. Today however I want to talk about doping

DOPING? YOU MEAN LIKE... DRUG DOPING??

Actually, you can kind of put it that way if you want, I’ll explain why but first we need to start off with the basics. Silicon bonds like this and forms a ‘square’ lattice.

Silicon lattice
Silicon lattice

This lattice is pretty nice and organised. All the electrons are bonded and it’s all nice and organised.

Shame if something were to…. completely destroy that! >: )  hehehe

Along comes Antimony (Sb). Or for that matter, any other element with 1 more valence (outer shell) electron than Silicon like phosphorous. The antimony atoms manage to replace some silicon atoms in this lattice. When they bond though, there is 1 spare electron and like in graphite, this electron is loose and free to roam around.

Antimony doped silicon lattice
Phosphorous doped silicon lattice

THIS ADDITION OF IMPURITIES INTO THE LATTICE IS CALLED DOPING

This particular doping of silicon is called n type doping, the n standing for negative, and negative because the dopant (impurity you added) gives extra electrons to the material.

COOL... UH, IS THAT IT??

Nope! You can also p dope or positive dope silicon too. Instead of adding an element with 1 extra valence electron than silicon, you add an element with 1 less valence electron than silicon. This is usually boron. Doing this means that there is 1 less electron and this forms a theoretical ‘electron hole’, a spot where an electron is missing.

Boron doped silicon lattice
Boron doped silicon lattice

This lack of electrons, or ‘excess’ of electron holes puts a positive charge on the material, hence it is p doped silicon.

AWESOME! WHAT CAN YOU USE IT FOR?

Well as I said before you can use it to make transistors, these guys.

Transistor diagram
pnp transistor diagram

WHAT'S SO COOL ABOUT THEM?

They can do 2 different things. They can act as a switch and as an amplifier. It takes a really small current at one end (the base) and produces a much bigger electric current from it (through the collector and emitter). Transistors use the same mechanism to work as a switch, a small current flowing to one end of the transistor produces a big current from another end of the transistor.

WHY IS THAT SO IMPORTANT?

A transistor can either be on; with a current running through them, or off; without current running through them. This means they can store 2 numbers; 1 and 0. This is the basis of all modern computing, ones and zeros. Binary code. Everything is powered by these little doped semiconductor sandwiches.

HOPE YOU FOUND THIS POST INTERESTING!

OVER AND OUT 🙂

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