Classification of Materials

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The materials are classified based on their conducting property.

Conductor-
Conductor is a material that easily conduct electrical current. There are plenty of free electrons available for electric conduction. In conductor,valence band & conduction band overlapped, So forbidden band gap don't exist.
Example - Copper, Aluminum, Iron etc.
Properties of conductor- 
(1) It is rigid, non directional & crystalline in nature.
(2) Conductivity is good.
(3) Low melting & boiling temperature.
(4) Valence band & Conduction band overlapped, So forbidden band gap don't exist.

Insulator-
An insulator is a material that don't conduct electrical current. In insulator, distance between valence band & conduction band is large, So no any electron can move to Conduction band.
Example - Rubber, wood
Properties of insulator- 
(1) The forbidden energy gap is very large.
(2) Valence band electrons are bound tightly to atom.
(3) The value of forbidden energy gap for an insulator will be 6eV.

Semiconductor-
Semiconductor are such material which have conductivity between conductor & insulator.
Example - Semiconductor can be pure elements such as Silicon & Germanium. or compound such as Gallium Arsenide & Cadmium Selenide.

Properties of Semiconductor-
(1) The forbidden energy gap is very small.
(2) The forbidden gap for Ge is 0.7eV where as for Si is 1.1eV.
(3) A semiconductor actually is neither an insulator, nor a good conductor.
(4) As the temperature increases, the conductivity of semiconductor increases.

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