The difference between an insulator and a semiconductor is

The difference between an insulator and a semiconductor is

Right Answer is:

All of the above


The main difference between an insulator and a semiconductor are

  1. Forbidden gap
  2. Number of free electrons
  3. Atomic structure
  • An insulator has a wider forbidden gap as compared to semiconductors.
  • The number of free electrons is less in insulators.
  • The atomic structure of the insulator and conductor is different.


⇒ In an insulator, the lower band is fined with electrons and the higher band is empty at 0 K.

⇒ The lower, filled band is called the valence band, and the upper, empty band is the conduction band. 

In an insulator, the energy gap between the valence band and conduction band is very large and approximately equal to 5 eV.

⇒  Therefore, very high energy is required to push the electrons to the conduction band.

⇒ For these reasons the electrical conductivity of the insulator is extremely small and may be regarded as nil under ordinary conditions  (room temperature).


⇒ Semiconductors have the same type of band structure as an insulator; but the energy gap is much smaller, on the order of 1 eV.

⇒ At low temperature, the valence band of a semiconductor is completely filled and the conduction band is completely empty.

⇒ Therefore, a semiconductor virtually behaves like an insulator at low temperatures. However, at room temperature, some electrons cross over to the conduction band giving little conductivity to the semiconductor.

⇒ As the temperature is increased more valence electrons cross over to the conduction band and conductivity increases.

⇒ This shows that the electrical conductivity of a semiconductor increases with the increase of temperature, i.e., a semiconductor has a negative temperature coefficient of resistance.

Atomic Structure

The degree of conductivity is determined as follows:

1. Atoms with fewer than four valence electrons are good conductors.

2. Atoms with more titian four valence electrons are poor conductors.

3. Atoms with four valence electrons are semiconductors.

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