Question

Phosphorus which is used as an impurity to produce an extrinsic semiconductor is a ______ impurity.

• A. Trivalent
• B. Divalent
• C. Tetravalent
• D. Pentavalent

Answer 1

The correct option is D Pentavalent

Phosphorous is a pentavalent impurity. Means it has 5 electrons in its valence shell. When added to pure (or intrinsic) semiconductor like (Si) which has four electrons in its valence shell. Phosphorous replaces four electrons of Si with its four electrons whereas one electron stays free.

Therefore the number of electrons increases when phosphorous is added as an impurity. So n-type extrinsic semiconductor is formed.