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Bipolar transistor question

  1. May 21, 2010 #1
    why we over dope one side of the transistor
    why it lookes like
    N+ P N

    why not just
    N P N
  2. jcsd
  3. May 21, 2010 #2
    To get high injection efficiency resulting in high beta value ("hfe" on data sheet). An "n-p-n" device would have a low beta, near 1, resulting in amplifiers with poor current gain. But an "n+-p-n" device has a large beta value, on the order of 50 to 500, resulting in amplifiers with high values of current gain.

    Did that help?

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