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Question
Why is the base of a transistor made thin and is lightly doped?
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Solution
The base of a transistor is lightly doped than the emitter and narrowed so that almost all electrons injected from the emitter (in a n-p-n transistor) diffuse right across the base to the collector junction without recombining with holes. In other words, the base width is kept smaller than the recombination distance. In addition, to improve emitter efficiency and common-base current gain α, the emitter is much more heavily doped than the base.
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