On the basis of band theory, differentiate between insulator, conductor and semiconductor.
Answers
Band theory and conductors, insulators and semi-conductors
Conductors
In a conductor there are no band gaps between the valence and conduction bands. In some metals the conduction and valence bands partially overlap. This means that electrons can move freely between the valence band and the conduction band.
The conduction band is only partially filled. This means there are spaces for electrons to move into. When electrons for the valence band move into the conduction band they are free to move. This allows conduction.
Two rectangular boxes, one above the other. The top box is labelled Conduction band (empty) and the bottom box Valence band. Between the two is a band labelled overlap (no band)
Insulators
An insulator has a large gap between the valence band and the conduction band.
The valence band is full as no electrons can move up to the conduction band. As a result, the conduction band is empty.
Only the electrons in a conduction band can move easily, so because there aren't any electrons in an insulator's conduction band, the material can't conduct.
Insulator band theory
Semiconductors
In a semiconductor, the gap between the valence band and conduction band is smaller. At room temperature there is sufficient energy available to move some electrons from the valence band into the conduction band. This allows some conduction to take place.
An increase in temperature increases the conductivity of a semiconductor because more electrons will have enough energy to move into the conduction band.
Semi conductor band theory
The difference between insulators and semiconductors is due to a small amount of impurity added to a semiconductor which affects the energy bands. This process is called doping
Answer:
In metals, the conduction band is either partially filled or the valence band is partially empty. There are electrons that behave as free electrons as they shift to higher energy levels by acquiring energy above the Fermi level in the conduction band. There is no forbidden energy gap in the metals. Since there is no forbidden gap, the number of electrons available for the conduction is more increasing the conductivity of the material. Metals behave as a conductor because of the movement of the free electrons when a small amount of electric current is applied.
In insulators, the valence band is completely filled while the conduction band is empty. This results in a large energy gap. Since the energy gap between the conduction band and the valence band is more, there is no movement of electrons from the valence band to the conduction band.
In a semiconductor, the valence band is completely filled with electrons while the conduction band is empty. The energy gap between the bands is less. For electrons to jump from the valence band to the conduction band, room temperature needs to be maintained. If the temperature is 0K, there is no transfer of electrons from the valence band to the conduction band.