PN Junction. Silicon vs Germanium

  1. When we connect P and N materials, electrons from N drift to P, thus create negative ions in P and positive ions in N.

    => electric field (barrier potential) must depend on an amount of electrons recombined with holes in P region.

    => The more electrons recombined, the more ions created, the more barrier potential.

    BUT! Silicon has 14 electrons and 4 on the 3d shell. Germanium has 32 electrons and 4 on the 4th shell.

    => at 25C degrees, electrons in N region in Germanium must have more energy than electrons in Silicon, because less energy required to remove electron from an atom => more electrons can drift to P region, thus barrier potential for Germanium should be higher, however

    Vbp Germanium = 0.3 V Vbp Silicon = 0.7 V

    why?

    P.S. I am talking about P doped and N doped silicon compared to the junction between P doped and N doped germanium
     
  2. jcsd
  3. DrDu

    DrDu 4,417
    Science Advisor

    The number of electrons which recombine does not depend on the number of valence electrons. The potential difference rather depends on things like the dielectric constant of the semiconductors and the effective mass of the charge carriers.
     
  4. Thanks DrDu!
     
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