Semiconductors contd.......

For metals, the valance and conduction bands can overlap. The electrons in the overlapping region of energy are conduction electrons. Since there is large number of conduction electrons, the metals are good conductors.

An intrinsic semiconductor is a pure semiconductor. for instance, a silicon crystal is an intrinsic semiconductor if energy energy atom in the crystal is silicon atom.

A pure semiconductor has a very small electrical conductivity at ordinary temperature however, its conductivity can be increased appreciably by adding a small amount of trivalent impurity or pentavalent impurity to it. The process of adding the impurity is called DOPING. & the impurity is called dopant. The semiconductors so obtained is called extrinsic semiconductor.

When a pentavalent impurity is added to a pure semi conductor crystal during a crystal growth, the resulting semiconductor crystal is called N- semiconductor.

When a trivalent impurity is added to a pure semiconductor crystal during crystal growth, the resulting semiconductor crystal is called a P- semiconductor.