Value of forbidden energy gap for semi conductor is:

CONCEPT:

• Forbidden energy gap (ΔEg): The energy gap between the conduction band and valence band is known as the forbidden energy gap i.e.,

ΔEg = (C.B)min - (V.B)max

• No free electron is present in the forbidden energy gap.
• The width of the forbidden energy gap depends upon the nature of the substance.
• As the temperature increases, the forbidden energy gap decreases very slightly.

EXPLANATION:

​EXPLANATION:

Conductors: 

• Conductors allow an electric current to flow through them. 
  • There is no forbidden gap between the valence band and conduction band which results in the overlapping of both the bands.
  • The number of free electrons available at room temperature is large. Ex. Gold, Aluminium, Silver, Copper, etc.

Insulators:

• These substances do not allow electricity to pass through them.
  • They have high resistivity and very low conductivity.
  • The energy gap in the insulator is very high up to 7eV.
  • The material cannot conduct because the movement of the electrons from the valence band to the conduction band is not possible. Ex. Glass, wood, etc.

Semiconductors: 

• Germanium and Silicon are the most preferable material whose electrical properties lie in between semiconductors and insulators. 
  • The energy band diagram of the semiconductor is shown where the conduction band is empty and the valence band is completely filled but the forbidden gap between the two bands is very small which is about 1eV.
• From the above explanation, it is clear that the forbidden energy gap in an intrinsic semiconductor is of the order of 1eV. Hence, option 1 is correct.