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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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The base of a transistor is _____ doped.
Heavily
Moderately
Lightly
None
Lightly
Quick Summary: The base of a Bipolar Junction Transistor (BJT) is intentionally made very thin and lightly doped compared to the emitter and collector regions. This specific design ensures that the majority of charge carriers injected from the emitter pass through the base to the collector with minimal recombination.
The base of a Bipolar Junction Transistor (BJT) is intentionally made very thin and lightly doped compared to the emitter and collector regions. This specific design ensures that the majority of charge carriers injected from the emitter pass through the base to the collector with minimal recombination.
IE=IB+IC
α=IEIC
In an NPN transistor, the base is P-type. Because it is lightly doped, the density of holes (the minority carriers in the base) is very low. This reduces the probability of electrons (injected from the emitter) recombining with holes in the base, which allows approximately 95% to 99% of the emitter current to reach the collector as the collector current (IC).
Base width is kept very thin to minimize recombination.
Emitter is the most heavily doped region to maximize charge injection.
Collector has the largest physical area to dissipate heat.
Light doping in the base ensures high current gain (β).
High current amplification factor (β)
Efficient charge carrier transport
Susceptibility to punch-through if base is too thin
High temperature sensitivity
Switching circuits
Signal amplification
| Feature | Emitter | Base |
|---|---|---|
Doping Level | Heavily | Lightly |
The emitter is heavily doped to provide a large number of majority carriers.
The collector is moderately doped and physically larger than the emitter to improve power handling capacity.
Option B (Moderately) is incorrect as it describes the collector region, not the base.
C is correct — The base of a BJT is lightly doped to minimize the recombination of charge carriers injected from the emitter.
Always remember the mnemonic: 'Emitter-Heavy, Base-Light, Collector-Moderate/Large' for BJT design parameters in exams.