sir/mam,how are you?? i am abhijit.i have a doubt that why is the base lightly doped?please enlighten me with an answer. thank you very much.

Base provides the proper junction for interconnection between emitter and collector. It is made thin and slightly doped so that the number of majority carriers is low. So less number of electron-hole recombination takes place and whole current emitted from the emitter with a slight difference is passed to the collector.