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How does the doping increase the conductivity of semiconductors?

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Conductivity of semiconductors are exceptionally low for practical use. Semiconductors are doped to generate either a surplus or deficiency in valence electrons depending on whether n-type semiconductors are required or p-type. An electron rich or electron deficient impurity as compared to the intrinsic semiconductor, silicon or germanium is used for doping. Electronic defects are introduced in them by such impurities.

  1. On doping silicon with electron rich impurities, the extra electron becomes delocalized increasing the conductivity of doped silicon. Hence silicon doped with electron-rich impurity is called n-type semiconductor due to the negatively charged electron. For ex. When group 15 elements are added to silicon
  2.  When silicon is doped with electron-deficit impurities to increase the conductivity through positive holes, this type of semiconductors are called p-type semiconductors. Ex. Addition of group 13 elements to group 14 element.

 

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