Difference between conductors semiconductors and insulators on the basis of energy band theory with diagram ?

Distinction between insulator, conductor and
Semiconductor

• There are difference between conductor, insulator and semiconductor-

1. Conductor-What is conductor?
   The conductor are those substance which have valence electron loosely in contact with the nucleus. Due to which they act as free carriers of electronic charge. In a very good conductor nearly 10^22 free electron are present per unit volume. It resistivity is nearly 10^-6 ohm-centimetre(ohm-cm).

1. Insulator- What is insulator?
   The insulator are those substance which have very few free electrons. In fact a perfect insulator will have no free electron,and its resistivity will be infinite .pratically in the nature no substance is perfectly insulator at room temperature. A very good insulator is as mica has a resistivity of the order of 10^13 ohms - centimetre.

1. Semiconductor- What is semiconductor?

The semiconductor which have resistivity between the conductor and the insulator are called semiconductors. The best semiconductor are Germanium,Silicon,Selenium etc.In the semiconductor the number of free electron per unit volume is the order of 10^13.

Hence it resistivity lies between 10 to 100 ohm - centimetre.Apart this there is are some more difference between the conductor and semiconductor. When the temperature of the conductor is increased its resistivity increase.

But when the temperature of a semiconductor is increased its resistivity decrease. Also in the semiconductor, if impurity is mixed from outside then its electrical conductivity is very much affected which is not found in the case of conductor.

Classification of solids on the basis of energy bands --

1. Valence band-

The energy band occupied by the valence electron is called balance band .

1. Conduction band-

The energy band of the higher energy level which is either empty or partially filled above the valence band is called conduction band.

1. Forbidden energy gap-

The Valence band and conduction band in the solid are usually separated by a definite energy gap. Electron cannot have energy corresponding to this energy gap and hence it is known as forbidden energy gap.

It is denoted by "Eg".

** Distinction between conductor semiconductor and insulator on the basis of energy band -

1. Metal or Conductors - What is conductor on the basis of energy band?

A solid in which valence band and conduction band overlap each other is known as metals or conductor . There is no Forbidden energy gap between the valence band and conduction band . In metals , the conduction band is partly filled. The electron in the field energy level require a very small amount of energy by ( thermal excitation) to move to the unfilld energy levels in the conduction band. In the presence of applied electric field , the electrons in the filled energy levels gain energy and move to the unfilled energy level in the conduction band.

The movement of electrons in the conduction band constitutes electric current. Thus metals are good conductor of electricity. A conductor in the conduction band are known as conduction electrons.

1. Insulator-What is insulator on the basis of energy band?

In insulators the valence band is completely filled with the electron and the conduction band is empty and both the bands are separated by the forbidden energy gap of 6 Energy volt(ev).

The insulator can conduct electric current only if the electron from the balance band can move to the conduction band .This can happen if energy gained by electron in the valence band is greater than the forbidden energy gap. But the electrons in the valence band have the energy is equal to 3/2 K = 0.025 electron volt (ev) (where K= Boltzman's constant) at the room temperature. This energy is very small as compared to the energy of the forbidden gap therefore the electron in the balance band cannot go to the conduction band and hence insulator can not conduct electric current.Therefore insulator is a bad conductor of electricity.

1. Semiconductor-What is semi-conductor on the basis of energy band?

The semiconductor are the material in which the forbidden energy gap between the valence band and the conduction band is very small. Germanium and silicon are the good example of semiconductor. In the case of Silicon the Forbidden gap energy gap (Eg) is 1.2ev (electron volt) and for Germanium is about 0.72(ev) electron volt.

At zero (0K) kelvin the electrons in the valence band do not have sufficient energy to jump the conduction band and hence semiconductor behaves as a insulator at zero kelvin.But the room temperature some of the electrons in the valence band have sufficient thermal energy to jump to the conduction band and semiconductor may conduct at room temperature.

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