When a pentavalent imputrity is added in Ge crystal then, what type of semiconductor is obtained ?

Options

A. a p-type
B. an n-type
C. intrinsic
D. none of these

Answer

To determine the type of semiconductor obtained when a pentavalent impurity is added to a germanium (Ge) crystal, we can follow these steps:

### Step 1: Understand the Structure of Germanium
Germanium is a group IV element with four valence electrons. In its crystalline form, each germanium atom forms covalent bonds with four neighboring germanium atoms.

**Hint:** Remember that the number of valence electrons determines how an atom bonds with others.

### Step 2: Identify the Pentavalent Impurity
A pentavalent impurity is an element that has five valence electrons. Common examples include nitrogen (N), phosphorus (P), and arsenic (As). When a pentavalent atom is introduced into the germanium crystal, it will replace one of the germanium atoms in the lattice.

**Hint:** Pentavalent impurities are also known as donor impurities because they donate extra electrons.

### Step 3: Analyze the Bonding
When a pentavalent impurity like arsenic is added to the germanium crystal, it will form four bonds with the surrounding germanium atoms using four of its five valence electrons. This leaves one electron from the arsenic atom unbonded.

**Hint:** Consider how many electrons are available for bonding and how many are left free.

### Step 4: Determine the Type of Semiconductor
The unbonded electron from the pentavalent impurity becomes a free charge carrier in the crystal. In this case, the majority charge carriers are free electrons. This type of semiconductor, which has an abundance of free electrons, is classified as an n-type semiconductor.

**Hint:** Recall that n-type semiconductors are characterized by free electrons as the majority carriers, while p-type semiconductors have holes as the majority carriers.

### Conclusion
When a pentavalent impurity is added to a germanium crystal, the resulting semiconductor is an **n-type semiconductor**.

**Final Answer:** The type of semiconductor obtained is n-type.

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