(1) Semiconductors : The substances like silicon, germanium which have poor electrical conductance at low temperature but the conductance increases with the increase in temperature are called semiconductors.
(2) Their conductivity lies between metallic conductors and insulators.
(3) The energy difference between valence band and conduction band is relatively small, hence the electrons from valence band can be excited to conduction band by heating.
(4) Types of semiconductors :
There are two types of semiconductors :
(a) Intrinsic semiconductor
(b) Extrinsic semiconductor
(a) Intrinsic semiconductor :
- A pure semiconductor material like pure Si, Ge which have a very low but finite electrical conductivity is called intrinsic semiconductor.
- The electrical conductivity of a semiconductor increases with the increase in temperature.
(b) Extrinsic semiconductor :
- Semiconductor doped with different element is called extrinsic semiconductor.
- By doping with elements like Ga or P, the electrical conductivity is increased.
