Distinguish between intrinsic and extrinsic semiconductor.

In intrinsic semiconductors, the conduction is because of the intrinsic processes characteristics of the crystal, without the influence of impurities. A pure crystal of silicon or germanium is an intrinsic semiconductor. The electrons that are excited from the top of the valence band to the bottom of the conduction band by the thermal energy are responsible for conduction. The number   of    electrons   excited across the  gap  can be  calculated   from  the  Fermi-Dirac probability distribution. In extrinsic semiconductors, the conduction is due to the presence of extraneous impurities. The process of deliberate addition of controlled quantities of impurities to a pure semiconductor is called doping. The addition of impurities markedly enhances the conductivity of a semiconductor.