Question

Account for the following:
(i) Conductivity of silicon increases on doping it with phosphorus

(ii) Schottky defects lower the density of related solids

Answer 1

(a) When silicon is doped with phosphorus, phosphorus leaves an extra electron in silicon atom. This free electron is free to move inside the crystal and increases its conductivity.

(b) In schottky defect, equal no of positive and negative ions leave their correct lattice point and go outside the lattice creating a pair of vacancy. The vacancies are then free to move about as their own entities. Normally, these defects will lead to a decrease in the density of the crystal.