Which of the following when added as an impurity into silicon produces n-type semicondutor ?

Options

A. P
B. Al
C. B
D. Mg

Answer

To determine which impurity added to silicon produces an n-type semiconductor, we need to understand the characteristics of n-type semiconductors and the role of impurities.

### Step-by-Step Solution:

1. **Understanding n-type Semiconductors**:
- n-type semiconductors are characterized by having an excess of electrons (negative charge carriers) and a deficiency of holes (positive charge carriers). The majority charge carriers in n-type semiconductors are electrons.

2. **Silicon Structure**:
- Silicon (Si) has four valence electrons and forms four covalent bonds with neighboring silicon atoms. This results in a stable crystal structure.

3. **Role of Impurities**:
- To create an n-type semiconductor, we need to introduce an impurity that has more than four valence electrons. This impurity will donate extra electrons to the silicon lattice.

4. **Identifying Suitable Impurities**:
- We need to consider which elements can be used as impurities:
- **Phosphorus (P)**: Has five valence electrons. When added to silicon, it donates one extra electron, thus creating an n-type semiconductor.
- **Aluminium (Al)**: Has three valence electrons. It cannot donate extra electrons and would create a p-type semiconductor instead.
- **Boron (B)**: Has three valence electrons. Similar to aluminium, it cannot donate extra electrons and would also create a p-type semiconductor.
- **Magnesium (Mg)**: Has two valence electrons. It also cannot donate extra electrons and would not create an n-type semiconductor.

5. **Conclusion**:
- The only suitable impurity from the options provided that can be added to silicon to produce an n-type semiconductor is **Phosphorus**.

### Final Answer:
Phosphorus (P) is the impurity that, when added to silicon, produces an n-type semiconductor.