Question

There is an increase in conductivity when Silicon is doped with Phosphorus. Give reason

Answer 1

Si has valency 4 and phosphorus has 5. When silicon is doped with phosphorus, there is left one extra electron of phosphorus which contributes to increased conductivity in the formed semiconductor. (n-type where electrons are majority charge carriers).

Answer 2

There is an increase in conductivity when Silicon is doped with Phosphorus  because :

Si  doped with P becomes N type semiconductor.

N type semiconductor is obtained by adding trace amount of VA group element like Phosphorous To Pure Silicon  By doping.

When P is added to Si , some of the Si in the crystal are replaced by P atoms.

P has 5 valence electrons. In that four valence electrons will be used for bonding with Si and fifth electron serves to conduct electricity.