Materials can be classified into three main categories on the basis of their electrical conductivity: conductors, semiconductors, and insulators. Conductors are the materials that easily allow the flow of electric current through them. Semiconductor materials have electrical conductivity between the conductors and the insulators. While insulators do not conduct electric current at all.
Conductors, semiconductors, and insulators can be differentiated on the basis of a number of factors like conductivity, resistivity, band structure, forbidden gap, band overlap, current flow, behaviour at 0K, and examples. Let’s see the actual difference between conductor, semiconductor and insulator.
Difference between Conductor, Semiconductor and Insulator in tabular form
| Conductor | Semiconductor | Insulator |
| Conductors are the materials that easily allow the flow of electric current through them. | Semiconductors are the materials that have their conductivity between the conductors and the insulators. | Insulators are the bad conductors of electricity or they do not conduct electric current through them. |
| Conductors have very high conductivity (10-7 Ʊ /m), thus they can easily conduct electric current. | The conductivity of semiconductors lies between those of conductors and insulators thus they can act as conductor and insulator at different conditions. | Insulators have very low conductivity. |
| Since the conductors have a positive value of temperature coefficient of resistance, the resistance of conductors increases with an increase in temperature. | Since the temperature coefficient of resistance is negative, therefore the resistance of semiconductors decreases with an increase in temperature. | Insulators have very high resistance which further decreases with temperature. |
| Conduction in conductors is due to the presence of free electrons in metal bonding. | Conduction in semiconductors is due to the movement of holes and electrons. | Since there are no electrons or holes in the insulator, therefore insulators do not conduct electric current. |
| For the conductors, the temperature coefficient of resistance is positive. | The value of the temperature coefficient of resistance is negative for the semiconductors. | For insulators, the temperature coefficient of resistance is negative. |
| The conduction and valence band overlaps for the conductors or there is no energy gap between the conduction and valence band. Therefore they do not require extra energy for the conduction state. | The conduction band and the valence band are separated by an energy gap of 1.1 eV. | The energy gap between the conduction band and valence band lies between 6eV to 10eV for the insulators. |
| The common examples of conductors are Copper, Aluminium, Gold, Silver, etc. | Silicon, Germanium, Arsenic are examples of Semiconductors. | The examples for insulators include paper, rubber, plastic, etc. |
What are conductors?
These are the materials that easily allow the flow of electric current through them. Most common electrical conductors are made from metals. The current flows in them due to the presence of free electrons or ions which start moving when a potential difference is applied across them.
Conductors like metals show electrical conductivity at room temperature which decreases with an increase in temperature. The electrical resistance of the conductors is very low i.e., they offer a very little amount of obstruction to the flow of current. The resistance of a conductor depends on the length, area, and nature of the conductor.
As the conduction and valence band overlaps in the conductors, whenever even a little amount of electric field is applied across them, the electrons easily move from the valence band to the conduction band due to the influence of the electric field. This movement of charge carriers generates a large electric current through them.
What are semiconductors?
Semiconductors are the materials that have their electrical conductivity between the conductors and the insulators. The charge carriers responsible for the flow of electric current are the electrons and holes.
Semiconductors have the ability to behave as conductors as well as insulators depending on the condition. The band gap of semiconductors is greater than the conductors but it is smaller than the insulators i.e 1eV. Therefore their electrons need a little amount of energy to push into the conduction state. At absolute zero temperature, no movement of charge carriers takes place in semiconductors, hence they behave as insulators. But at room temperature, enough energy is available to displace a few electrons from the valence band to the conduction band.
What are insulators?
These are the materials that do not allow the flow of electric current through them. These are not good conductors of electric charges. The energy band gap is so high for the insulators that even the applied potential difference cannot excite the electrons from the valence band to the conduction band.
Since the temperature coefficient of resistance is negative for the insulators, hence the resistance offered by the insulators decreases with an increase in temperature.
Conclusion
From the above discussion, we have concluded that the responsible factor for the flow of electric current through the materials is the movement of electrons from the valence band to the conduction band. The band gap of conductors is very small therefore they are good conductors and possess high conductivity, while semiconductors have a small band gap, therefore their conductivity lies between those of conductors and insulators. The band gap of insulators is very large therefore insulators do not conduct electric current.
Author
Deepak Yadav
Aligarh Muslim University, Aligarh
