1. Tardigrade
  2. Question
  3. Chemistry
  4. Assertion: Conductivity of silicon increases by doping it with group-15 elements. Reason: Doping means introduction of small amount of impurities like P, As or Bi into the pure crystal.

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Q. Assertion : Conductivity of silicon increases by doping it with group-15 elements.
Reason : Doping means introduction of small amount of impurities like $P, As$ or $Bi$ into the pure crystal.

AIIMSAIIMS 2010The Solid State

Solution:

When a silicon crystal is doped with a group-15 elements, such as $P, A s, S b$ or $B i$ the structure of the crystal lattice is left unchanged but an occasional atom with five valence electrons occupies a site that would normally be occupied by a silicon atom. The foreign atom uses four of its electrons in covalent bonding but the remaining fifth electron becomes delocalised and is thus free to contribute to electrical conduction.