Question

The material with a band gap of 0 eV is

• A. Metal
• B. Semiconductor
• C. Insulator
• D. Dielectric

Hint:

Because metals have a band gap of \( 0 \text{ eV} \), they do not show an increase in free-carrier concentration with temperature, unlike semiconductors whose conductivity increases with temperature.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks to identify the class of materials that has a band gap energy (\( E_g \)) of exactly \( 0 \text{ eV} \).

Step 2: Detailed Explanation:

• Band Theory of Solids: According to the electronic band theory of solids, electrons occupy energy bands separated by forbidden energy gaps (band gaps).
The band gap is the energy difference between the top of the filled valence band and the bottom of the empty conduction band.

• Electronic Structure of Metals: In metals (conductors), there is no forbidden gap separating the valence and conduction bands.
Instead, the valence and conduction bands overlap, or the valence band is only partially filled.
This results in a band gap of exactly \( 0 \text{ eV} \), allowing free electrons to move easily under an applied electric field, which explains why metals have high electrical conductivity.

• Comparison with Other Classes:
-

Semiconductors (Option B) have a narrow, non-zero band gap, typically in the range of \( 0.5 \text{ to } 3 \text{ eV} \).
-

Insulators and

dielectrics (Options C and D) have wide band gaps, typically greater than \( 4 \text{ to } 5 \text{ eV} \), which prevents thermal excitation of electrons from the valence band to the conduction band at room temperature.


Step 3: Final Answer:
Thus, the material with a band gap of 0 eV is a Metal, corresponding to Option (A).