Topic: Electronic Devices and Circuits
If a donor type impurity is added to the semiconductor, then at a given temperature, the Fermi Level
- A. Moves towards the center of the energy gap
- B. Moves towards the valence band
- C. Moves towards the conduction band
- D. Doesn't change
Answer: C. Moves towards the conduction band
Explanation: The Fermi level position is given by $E_C - E_F = kT \ln\left(\frac{N_C}{N_D}\right)$. As the donor concentration ($N_D$) increases, the term $kT \ln\left(\frac{N_C}{N_D}\right)$ decreases, which means the difference between $E_C$ and $E_F$ becomes smaller. Thus, the Fermi level moves towards the conduction band.