In a bipolar junction transistor

In a bipolar junction transistor

all the three regions (the emitter, the base and the collector) have equal concentrations of impurity
the emitter has the least concentration of impurity
the collector has the least concentration of impurity
the base has the least concentration of impurity
This question was previously asked in
UPSC CDS-2 – 2016
In a bipolar junction transistor (BJT), the base region has the least concentration of impurity.
– A BJT consists of three semiconductor regions: the emitter, the base, and the collector, separated by two p-n junctions.
– These regions are doped with impurities (donors or acceptors) to create n-type and p-type semiconductors.
– The doping levels are designed specifically for the transistor’s operation:
– Emitter: Heavily doped (high concentration) to efficiently inject charge carriers (electrons or holes) into the base.
– Base: Lightly doped (low concentration) and made very thin to allow most injected carriers from the emitter to reach the collector and to minimize recombination within the base.
– Collector: Moderately doped (intermediate concentration, less than emitter but more than base) and typically larger in size to collect the carriers from the base and dissipate heat.
The doping profile and physical geometry of the emitter, base, and collector regions are crucial for the performance of a bipolar junction transistor, determining its gain, operating speed, and power handling capabilities.