As we know, for Bi-polar junction transistor

The length of each section of transistor is in order as shown above,

i,e., Lc > L E > L B

and doping profile is Emitter > Collector > Base

Whereas, for transistor action Base-emitter junction is forward biased and Base-collector junction is reversed biased.

Hence from this we can conclude that, for transistor action the base region must be very thin and lightly doped.

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