Which of the following is an n-type semiconductor ?

Options

A. Si doped with Ga
B. Si doped with In
C. Ge doped with As
D. Ge doped with Ga

Explanation

To determine which of the following is an n-type semiconductor, we need to understand the concept of n-type semiconductors and how they are formed.

### Step-by-Step Solution:

1. **Understanding n-type Semiconductors**:
- n-type semiconductors are formed when a group 14 element (which has 4 valence electrons) is doped with a group 15 element (which has 5 valence electrons). The extra electron from the group 15 element contributes to electrical conductivity.

2. **Identifying Group Elements**:
- Group 14 elements include: Carbon (C), Silicon (Si), Germanium (Ge), Tin (Sn), and Lead (Pb).
- Group 15 elements include: Nitrogen (N), Phosphorus (P), Arsenic (As), Antimony (Sb), and Bismuth (Bi).

3. **Analyzing the Options**:
- We need to look at the options provided to identify which one involves a group 14 element doped with a group 15 element.
- If an option has a group 14 element doped with a group 13 element, it will form a p-type semiconductor instead.

4. **Evaluating Each Option**:
- **Option 1**: Silicon (Si) doped with Germanium (Ge) - Both are group 14 elements, so this is not n-type.
- **Option 2**: Gallium (Ga) doped with Silicon (Si) - Gallium is a group 13 element, so this is also not n-type.
- **Option 3**: Silicon (Si) doped with Arsenic (As) - Silicon is a group 14 element and Arsenic is a group 15 element, making this an n-type semiconductor.
- **Option 4**: Gallium (Ga) doped with Germanium (Ge) - Again, this involves a group 13 and group 14 element, so this is not n-type.

5. **Conclusion**:
- The correct answer is **Silicon doped with Arsenic** (Option 3), which is an n-type semiconductor due to the presence of excess electrons contributed by the arsenic.

### Final Answer:
**Silicon doped with Arsenic is an n-type semiconductor.**

---