Which of the following statements are true about semiconductors ?

Options

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

Answer

To determine which statements about semiconductors are true, we will analyze each statement one by one.

### Step 1: Analyze the first statement
**Statement:** Silicon doped with electron-rich impurity is a p-type semiconductor.

- **Explanation:** Silicon (Si) is a group 14 element with four valence electrons. When silicon is doped with an electron-rich impurity (such as phosphorus), it gains extra electrons, which leads to the formation of an n-type semiconductor. Therefore, this statement is **false**.

### Step 2: Analyze the second statement
**Statement:** Silicon doped with electron-rich impurity is an n-type semiconductor.

- **Explanation:** As established, when silicon is doped with an electron-rich impurity, it gains additional electrons. This results in the formation of an n-type semiconductor, characterized by an abundance of negative charge carriers (electrons). Therefore, this statement is **true**.

### Step 3: Analyze the third statement
**Statement:** Delocalized electrons increase the conductivity of the doped silicon.

- **Explanation:** Delocalized electrons are free to move within the semiconductor. In doped silicon, the presence of more electrons (due to doping) enhances the conductivity because more charge carriers are available to conduct electricity. Thus, this statement is **true**.

### Step 4: Analyze the fourth statement
**Statement:** An electron vacancy increases the conductivity.

- **Explanation:** An electron vacancy, often referred to as a "hole," represents a lack of an electron. While holes can contribute to conductivity in p-type semiconductors, the statement as it stands is misleading. The presence of holes alone does not increase conductivity; it is the delocalized electrons that primarily enhance conductivity. Therefore, this statement is **false**.

### Conclusion
Based on the analysis:
- **True Statements:**
- Silicon doped with electron-rich impurity is an n-type semiconductor.
- Delocalized electrons increase the conductivity of the doped silicon.

- **False Statements:**
- Silicon doped with electron-rich impurity is a p-type semiconductor.
- An electron vacancy increases the conductivity.

### Final Answer
The true statements about semiconductors are:
1. Silicon doped with electron-rich impurity is an n-type semiconductor.
2. Delocalized electrons increase the conductivity of the doped silicon.

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