BIPOLAR JUNCTION TRANSISTORS

 The bipolar junction transistor is constructed with three-doped semiconductor regions separated by two PN junctions. 


The three regions are called 


a.    Emitter

b.    Base

c.    Collector. 








The two types of bipolar transistors are 
(a). One type consists of two N-regions separated by a P-region (NPN),
 and the other consists of two P-regions separated by an N-region (PNP). 
The PN junction joining the base region and the emitter region is called the base-emitter junction. 

The junction joining the base region and the collector region is called the base-collector region. A wire lead connects to each of the three regions. 

These leads are labeled E, B, and C for the emitter, base, and collector, respectively. The base material is lightly doped and very narrow compared to the heavily doped emitter and collector materials. 
the schematic symbols for the NPN and PNP bipolar transistors. The term bipolar refers to the use of both holes and electrons as carriers in the transistor structure. 



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