Which of the following statements are ture about semi-conductors ?

Options

A. Silicon doped with electron rich impurity is a p-type semi-conductor
B. Silicon doped with an electron rich impurity is an n-type semi-conductor
C. Delocalised electrons increase the conductivity of doped silicon
D. An electron vacancy increases the conductivity of a-type semi-conductor.

Explanation

To determine which statements about semiconductors are true, we will analyze each option based on our understanding of semiconductor doping and properties.

### Step-by-Step Solution:

1. **Understanding the Types of Semiconductors**:
- Semiconductors can be classified into two main types based on the type of impurity used for doping: n-type and p-type.
- **n-type semiconductors** are created by doping a pure semiconductor (like silicon) with an electron-rich (pentavalent) impurity, such as phosphorus. This introduces extra electrons into the material.
- **p-type semiconductors** are formed by doping with an electron-deficient (trivalent) impurity, such as aluminum, which creates "holes" (absence of electrons) in the structure.

2. **Analyzing Each Statement**:
- **Statement 1**: "Silicon doped with electron-rich impurity is a p-type semiconductor."
- This statement is **false**. Silicon doped with an electron-rich impurity (like phosphorus) forms an n-type semiconductor, not a p-type.

- **Statement 2**: "Silicon doped with an electron-rich impurity is an n-type semiconductor."
- This statement is **true**. As explained, doping silicon with a pentavalent impurity results in an n-type semiconductor.

- **Statement 3**: "Delocalized electrons increase the conductivity of doped silicon."
- This statement is **true**. The presence of free (delocalized) electrons in n-type semiconductors increases conductivity.

- **Statement 4**: "An electron vacancy increases the conductivity of a p-type semiconductor."
- This statement is **false**. While electron vacancies (holes) do contribute to conductivity in p-type semiconductors, the statement is misleading as it implies that the vacancy itself increases conductivity rather than the movement of holes.

3. **Conclusion**:
- The true statements about semiconductors are:
- **Statement 2**: Silicon doped with an electron-rich impurity is an n-type semiconductor.
- **Statement 3**: Delocalized electrons increase the conductivity of doped silicon.

### Final Answer:
The true statements about semiconductors are **B** and **C**.