Question

Which of the following impurity should be doped with silicon to give p-type semiconductor?

Answer 1

Semiconductors can be dopped with trace elements of higher or lower valency.
Silicon belongs to the carbon family having four valence electrons. Each silicon is bonded to four other silicon atoms.
When small amount of trivalent element ( boron) is added, all three valence electrons form bond with three silicon atoms and a positive hole is created. The positive hole is free to move and can enhance the electrical conductivity of silicon through positive hole conduction mechanism.
Such semiconductors are called as p-type semiconductor.
Phosphrous and arsenic are pentavalent, when these impurities are added to silicon it creates extra electrons and cause n-type semiconductors.
Germanium being of the silicon family will not produce extra electrons or positive holes.
Hence, option (b) is correct.