Which of the following is NOT a trivalent impurity?

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ALP CBT 2 Electrician Official Paper (Held On: 23 Jan 2019 Shift 3)
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  1. Boron
  2. Phosphorus
  3. Indium
  4. Gallium

Answer (Detailed Solution Below)

Option 2 : Phosphorus
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Important Points:

  • P-type semiconductor: The semiconductor having holes as majority charge carriers and electrons as a minority charge carrier is called as P-type semiconductor.
  • Extrinsic N-Type Semiconductor is formed when a trivalent impurity is added to a pure semiconductor.
  • Example of trivalent impurity are BoronGallium and Indium
  • Trivalent impurity like boron, have 3 valence electrons
  • Each atom of the impurity fits in the silicon crystal by forming covalent bonds with the surrounding silicon atoms
  • The dopant boron atom has one less electron than surrounding silicon and thus vacancy is generated that acts as a hole.


F1 U.B. N.J. 10.09.2019 D 4

N-type semiconductor: The semiconductor having electrons as majority charge carriers and holes as a minority charge carrier are called as N-type semiconductor.

  • When pentavalent impurity is doped in intrinsic semiconductor then we got N-type semiconductor. For example: Arsenic, Phosphorus etc.
 
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