Difference between conductors, Insulators and semiconductors
All solid materials are basically divided into four types based on their electrical properties. They are
- Insulators(poor or very bad conductors)
- Metals (Good conductors)
- Semiconductors(partialy conducts)
- Super conductors(Good conductor it has zero resistance)
Insulators are bad conductors of electricity. In insulator valence band energy levels are filled and conductors band levels are empty.Here conduction band is much above the valence band.The energy difference between the conduction band and valence band is called forbidden gap.In the case of insulating material forbidden gap is large.At insulator at ordinary temperature the electronics cannot get sufficient energy for jump into conduction band in order to conduct electricity.
In metals valence band and conduction bands are overlap.The electrons in the upper region of valence band are in the upper region of valence band are in the conduction band itself.They can easily move inside the solid.The electrons which present in conduction band are called conduction electrons..Here forbidden gap is extremely thin.The upper most energy bands of metals are only partially filled.This partially filled band to gain small amount of energy from the electric field and so to be promoted to the conduction band.
Semiconductors conductivity lies between insulators and conductors.Here the forbidden gap is very small. In semiconductor both electrons and holes are charge carriers .The electrons and holes are move randomly in the semiconductor.When an external voltage is given to the semiconductor at that time electrons and holes drift in opposite directions and produces a current flow.The current through semiconductor is the combined effect of the drift of electrons and holes.Semiconductor has a variation of electrical resistivity with temperature.