Question

Fermi level of energy of an intrinsic semiconductor lies

• A. in the middle of the forbidden gap.
• B. below the middle of forbidden gap.
• C. above the middle of forbidden gap.
• D. outside the forbidden gap.

Answer 1

Answer: (A)

in the middle of the forbidden gap.

Fermi energy is determined as the energy point where the probability of occupancy by an electron is exactly $50$ or $0.5$, i.e., $\frac{1}{2}$. For the intrinsic semiconductor, since electrons and holes are always created in pairs, $n=p=ni$. Hence, there are equal number of holes and electrons in valence band and conduction band respectively. Therefore, the Fermi energy level lies in the middle of the forbidden gap, i.e., energy band gap.