How do NPN and PNP transistors work. I understand n-type materials and p-type materials as well as the workings of a p-n junction in terms of doping and electrons and electron holes working as charge carriers.

 

Jack

So are you asking about how they work in terms of operation in a circuit?

a transistor is basically a diode between the base and emitter.

a reverse bias accross these causes the electrons to form a gap across the junction due to doping etc. this gap or "depletion zone" is an excellent insulator.

 

when the base-emitter is forward biased, current flows across this junction.

the transistor effect is due to a slightly different type of connection between the base and collector. here, the electrons can flow relatively freely.

the voltage across the collector-emitter can pass through the base and the depletion zone only if the depletion zone is conductive.

 

i'm not entirely sure on how the connections differ between the layers nor how the depletion zone operates under high forward collector voltages.

Given the forum and general stuff in the OP I suspect they are more interested in their physical origins of the pnp and npn junctions leading to their effect.

 

I don't have much time to explain them atm, got exams shortly. But a quick google:

 

http://www.ph.ed.ac.uk/~jsl/lecture7.pdf

http://en.wikipedia.org/wiki/Bipolar_junction_transistor