Which of the following statements is true for an N-type semiconductor

Options

A. The donor level lies closely below the bottom of the conduction band
B. The donor level lies closely above the top of the valence band
C. The donor level lies at the halfway mark of the forbidden energy gap
D. None of above

Explanation

To determine which statement is true for an N-type semiconductor, we need to understand the characteristics of N-type semiconductors and the position of the donor energy level.

### Step-by-Step Solution:

1. **Understanding N-type Semiconductors**:
- N-type semiconductors are formed by doping a pure semiconductor (like silicon or germanium) with a pentavalent impurity (like arsenic).
- The pentavalent atom has five valence electrons, four of which form bonds with the semiconductor atoms, while the fifth electron becomes free to conduct electricity.

2. **Energy Bands in Semiconductors**:
- In semiconductors, there are two main energy bands: the valence band and the conduction band.
- The conduction band is the higher energy band where free electrons can move and conduct electricity, while the valence band is the lower energy band filled with electrons.

3. **Donor Energy Level**:
- When a pentavalent atom is introduced into the semiconductor, it creates a donor energy level.
- This donor energy level is associated with the extra electron that is not involved in bonding.

4. **Position of the Donor Level**:
- The donor energy level lies just below the conduction band. This means that the energy required for the donor electron to jump into the conduction band is relatively small.
- Therefore, the correct statement regarding the position of the donor level in an N-type semiconductor is that it lies closely below the bottom of the conduction band.

5. **Evaluating the Given Statements**:
- **Statement 1**: The donor level lies closely below the bottom of the conduction band. (True)
- **Statement 2**: The donor level lies closely above the top of the valence band. (False)
- **Statement 3**: The donor level lies at the halfway mark of the forbidden energy gap. (False)
- **Statement 4**: None of these. (False)

### Conclusion:
The true statement for an N-type semiconductor is that the donor level lies closely below the bottom of the conduction band.