The donor impurity to be added for doping germanium crystal, will be of valency

Options

A. 2
B. 3
C. 4
D. 5

Answer

To determine the valency of the donor impurity that should be added for doping a germanium crystal, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Doping**: Doping is the process of adding impurities to a semiconductor to change its electrical properties. There are two types of doping: n-type and p-type.

2. **Identify the Type of Doping**: In this question, we are concerned with donor impurities, which are typically associated with n-type doping. Donor impurities provide extra electrons to the semiconductor.

3. **Know the Valency of Germanium**: Germanium (Ge) is a group IV element, which means it has 4 valence electrons.

4. **Determine the Valency of Donor Impurities**: Donor impurities are usually pentavalent, meaning they have 5 valence electrons. When a pentavalent atom (like phosphorus, arsenic, or antimony) is introduced into the germanium crystal, it forms covalent bonds with the germanium atoms.

5. **Analyze the Bonding**: When a pentavalent atom bonds with germanium, it shares 4 of its electrons with the 4 valence electrons of germanium. However, it has one extra electron that does not participate in bonding. This extra electron becomes free and acts as a charge carrier.

6. **Conclusion**: Since pentavalent atoms have a valency of 5, the correct answer to the question is that the donor impurity to be added for doping germanium crystal will have a valency of 5.

### Final Answer:
The donor impurity to be added for doping germanium crystal will be of valency 5.

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