BJT(Bipolar Junction Transistor) Bipolar :- Conduction due to both holes and electron. Diode is also a bipolar device. BJT is a bi-junction transistor i.e. it has two PN Junction inside. BJT has three terminals: a) Emitter b) Base c) Collector BJT Diagram Emitter is most heavily doped because it is the source of all charge carries (NE > 10^18) Base is moderately doped but it is made thin so that charges carriers entering from emitter are able to reach collector and very few charges recombined in base. Usually collector base junction is kept reverse biased therefor depletion layer exist. Due to less doping of collector region compare to base depletion layer extend more into collector. If (doping base) NB < NC then depletion layer extends more into base than collector and can completely depletion base due to less width called as punch through. But collector must also be heavily doped to increase conductivity...