Question

When a solid with a band gap has a donor level just below its empty energy band, the solid is

• A. an insulator
• B. a conductor
• C. a p-type semiconductor
• D. an n-type semiconductor

Hint:

Donor impurity introduces an energy level near conduction band, making electrons the majority carriers \(\Rightarrow\) n-type semiconductor.

Answer 1

The Correct Option is D

Step 1: Understand donor level position.
A donor level lies just below the conduction band and donates electrons easily to the conduction band.
Step 2: Effect of donor impurity.
When electrons are donated, the conduction band gets extra electrons, increasing conductivity.
Step 3: Identify majority charge carriers.
Since electrons become majority carriers, the material becomes an n-type semiconductor.
Step 4: Match with option.
Thus, correct option is (D).
Final Answer:
\[ \boxed{\text{(D) an n-type semiconductor}} \]