Class 12 Physics Semiconductor Electronics n-type semiconductor

n-type semiconductor

  • When pure Si or Ge which has four valency electrons is doped with controlled amount of pentavalent atoms, like Arsenic, Phosphorus, Antimony or Bismuth, we get a n-type semiconductor
  • The four valence electron from the impure atom will combine with four electrons of the Si or Ge atom to form 4 covalent bonds
  • The fifth electron of the impure atom is free to move. Thus, each atom of the impure substance, donates a free electron for conduction. Hence, it is called as donor atom
  • Giving the free electron for conduction, the impure atom becomes positively charged, giving rise to a hole
  • Thus in n-type semiconductors, electrons are the majority carriers and holes are minority carriers

  

Energy band theory

  • Comparing Si or Ge doped with impurities like Arsenic with a pure Si or Ge,  the lowest energy level  of the conduction band  is less
  • The electrons occupy discrete energy levels called the donor energy level between the valence band and the conduction band
  • This donor energy level is below the bottom of the conduction band
  • Thus, very small energy supplied can excite the electron from the donor level to the conduction band, hence, conductivity of semiconductor becomes remarkably improved

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