Which of the following statements is correct regarding the doping levels of the emitter, base and collector regions in a bipolar junction transistor (BJT)? 

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SSC JE Electrical 4 Dec 2023 Official Paper II
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  1. The doping levels of the emitter, base and collector are all the same. 
  2. The emitter is lightly doped, the base is heavily doped and the collector is moderately doped. 
  3. The emitter is moderately doped, the base is heavily doped and the collector is lightly doped. 
  4. The emitter is heavily doped, the base is lightly doped and the collector is moderately doped. 

Answer (Detailed Solution Below)

Option 4 : The emitter is heavily doped, the base is lightly doped and the collector is moderately doped. 
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Detailed Solution

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Explanation:

The correct statement regarding the doping levels of the emitter, base, and collector regions in a bipolar junction transistor (BJT) is: The emitter is heavily doped, the base is lightly doped, and the collector is moderately doped.

  • This doping profile is typical for an NPN (negative-positive-negative) BJT.
  • The heavily doped emitter facilitates efficient injection of majority carriers into the base, while the lightly doped base allows for the transit of minority carriers across the base region.
  • The moderately doped collector helps in the collection of majority carriers that have crossed the base.
  • This specific doping arrangement is essential for the proper operation of the transistor in amplification and switching applications.
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