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Kirk Effect

  1. Mar 2, 2014 #1
    Hello folks,

    I'm trying to understand the Kirk Effect in BJTs. I have read some articles published in IEEE and in my semiconductor device physics textbooks, but they don't offer a good qualitative analysis. The difficulty I'm having is trying to understand how the base widens as a result of high current.

    So far, I have understood it as far as follows. We'll assume NPN transistors. The base-collector depletion region mostly exists in the collector because of its light doping. When a current is flowing (minority charge carriers, electrons, diffusing from base to collector) there is a constant current density in the depletion region due to velocity limitations. When the current increases, so does the current density in the depletion region and when this current density approaches the doping density of the collector, the depletion region ceases to exist in the collector. I believe that it ceases to exist when the current density approaches the doping density because the ionized donors and the electrons cancel out. Am I correct?

    A depletion region requires ionized donors and acceptors. Due to the high current density, the ionized donors cease to exist, but what happens to the ionized acceptors which are on the base side of the depletion region?

    How does the base widen?

    Thanks for helping me out.
     
  2. jcsd
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