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Homework Help: Static current gain of BJT?

  1. May 14, 2009 #1
    static current gain of BJT????????

    to increase the static current gain of a BJT what should i do ?////////

    1.base is made thin and heavily doped
    2. collector is made thick and heavily doped
    3.base is made thin and lightly doped
    4.emitter is made thin and heavily doped

    its an MCq question so i dont have any kind of pre works to show u hope that someone will help me with an answer with a valid reason.
  2. jcsd
  3. Jun 20, 2010 #2
    Re: static current gain of BJT????????

    making thin and lightly doped base,
    the recombination will be much less.
    amount of current coming from collector to emitter (or reverse),will be more and gain will be more.

    *the main problem for currebt gain is recombination.
    thin base means less area for recombination,
    less doping also means so.

    **for MCQ question,
    this is the most likely factor,than others.
  4. Jun 20, 2010 #3


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    Science Advisor

    Re: static current gain of BJT????????

    Actually, in today's bipolar transistors, the base is so thin that there is very little recombination. So the current gain is almost completely determined by the emitter efficiency. That is (for an NPN transistor) how much of the emitter current is composed of electrons injected from the emitter into the base , and how much is composed of holes injected from the base into the emitter. The higher the ratio of these two currents, the higher the gain. This ratio is determined by the ratio of emitter doping to base doping, so a heavily doped emitter and lightly doped base increases the current gain.
  5. Jun 20, 2010 #4
    Re: static current gain of BJT????????

    this answer is really more practical and right than mine.
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