Class 12 Physics Semiconductor Electronics p-type semiconductor

p-type semiconductor

  • When pure Si or Ge which has four valency electrons is doped with controlled amount of trivalent atoms, like Gallium, Indium, Boron or Aluminium, we get a p-type semiconductor
  • The three valence electron from the impure atom will combine with three electrons of the Si or Ge atom to form 3 covalent bonds
  • There will be one unbounded electron in the Ge atom which would try to form a covalent bond with the neighbouring Ge atom
  • This Ge-Ge covalent bond creates a deficiency of electron in Ge atom. Thus, creating a hole
  • This hole is compensated by the breakage of Ge-Ge covalent bond in the neighbourhood. Hence, electron moves towards the hole, resulting in hole formation at some other place
  • The trivalent atoms are called acceptor atoms and conduction of electricity is due to the motion of holes
  • Thus in p-type semiconductors, holes are the majority carriers and electrons are minority carriers

Energy band theory

  • Si or Ge doped with impurities like Aluminium, produces energy level which is situated in the energy gap slightly above the valence band
  • This is called as acceptor energy level
  • At room temperature, the electrons in the valence band can easily be transferred to the acceptor level. This produces a large number of holes in the valence band.
  • The valence band becomes the hole conducting band

 

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