Bipolar Junction transistors(Basic)

A bipolar junction transistor(BJT) has three differently doped region where the n-type semiconductor may be sandwiched between two p-type semiconductors or the opposite thus giving it a common name as PNP or NPN transistor.The semiconductor material which is sandwiched is very small and is coated with plastic materials to protect it with moisture.

The above diagram which you can see is PNP transistor consisting of emitter region,base region and collector region.

Emitter(E)- The above figure indicates where emitter region is placed,this region is responsible for providing charge carriers to the base and collector regions.The emitter region is always denser as compared to the other regions as it is always heavily doped.

Base (B)-As mentioned earlier base region is situated in the middle of two p or n-type semiconductors.The base region is a thin region and always lightly doped.

Collector(C)-The position of collector region is clearly indicated by the diagram.The name is so given as it collects charge carriers.The collector region is comparatively bigger than emitter region(not indicated in the diagram correctly).The doping level of collector is less than the emitter but it is more than the base region.The above transistor has two junctions namely emitter-base junction(JE) and collector base junction(Jc).

SYMBOL(NPN only)-

The arrow head on the emitter terminal represents the flow of current.This above post only gives you the basic framework of bipolar junction transistor.Working and biasing will be taken up by subsequent posts.Until then Happy Reading!!