Question

On adding a little phosphorus to silicon, we get a/an:

• A. n-type semiconductor
• B. p-type semiconductor
• C. metallic conductor
• D. insulator

Answer 1

The correct option is A n-type semiconductor

Silicon and germanium belong to group 14 of the periodic table and have four valence electrons each. In their crystals, each atom forms four covalent bonds with its neighbours. When doped with a group 15 elements like P or As, which contains five valence electrons, they occupy some of the lattice sites in silicon or germanium crystal.

Four out of five electrons are used in the formation of four covalent bonds with the four neighbouring silicon atoms. The fifth electron is extra and becomes delocalised.

These delocalised electrons increase the conductivity of doped silicon(or germanium). Here, the increase in conductivity is due to the negatively charged electron. Hence, silicon doped with an electron-rich impurity is called n-type semiconductor.