Question: Why can't you make a transistor using two identical diodes?

Robert Thompson answered on 21 Mar 2012:

Hey ok, This isn’t an easy question to answer. The problem is to do with how much energy an electron needs to have if it is any part of the transistor….. bare with me….

We are here talking about Bi-Polar transistors which have an n part, a p part and then a n part again – npn,

The electron needs less energy to be in n than p. The electron doesn’t want to move from n to p (because that would require energy), so what we do is add a voltage to p (this is the base current) and this lowers the energy the electron needs to go into p and a current can flow from n to p. Now we want the electron to flow into the the next n bit, so the energy here needs to be lower again.

If it was identical to the first n the electron flow wouldn’t happen efficiently. So what we do is we make it a slightly different n, this means now the electron doesn’t need as much energy to be in the final n bit, so wants to move into here.

So electron start in the first n, we lower the energy level of p so it wants to flow into here, and then we make sure the energy level of the second n is even lower so it will quickly move into here and flow into the rest of the circuit.

It’s very hard for me to explain just with text, I’m sorry