The valance of the impurity atom that is to be added to germanium crystal so as to make it a `N`-type semiconductor, is

Options

A. 6
B. 5
C. 4
D. 3

Answer

To determine the valency of the impurity atom that should be added to germanium to create an N-type semiconductor, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding N-type Semiconductors**:
- N-type semiconductors are formed when a semiconductor material, like germanium, is doped with an impurity that has more valence electrons than the semiconductor itself.

2. **Valency of Germanium**:
- Germanium (Ge) is a group 14 element and has a valency of 4, meaning it has 4 electrons in its outermost shell.

3. **Choosing the Right Impurity**:
- To create an N-type semiconductor, we need to add a pentavalent impurity. Pentavalent impurities have 5 valence electrons.

4. **Identifying Pentavalent Elements**:
- Pentavalent elements are found in group 15 of the periodic table. Examples include nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi).

5. **Conclusion**:
- Since we need to add an impurity with 5 valence electrons to germanium, the valency of the impurity atom that should be added is 5.

### Final Answer:
The valency of the impurity atom that is to be added to germanium crystal to make it an N-type semiconductor is **5**.

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