silicon doped with electron rich impurity forms ………. .

Options

A. p-type semiconductor
B. n-type semiconductor
C. intrinsic semiconductor
D. insulator.

Explanation

To solve the question "Silicon doped with electron rich impurity forms ……….," we will follow these steps:

### Step 1: Understand the Concept of Doping
Doping is the process of adding impurities to a pure semiconductor to modify its electrical properties. There are two types of dopants: electron-rich (n-type) and electron-deficient (p-type).

**Hint:** Remember that n-type semiconductors are formed by adding electron-rich impurities, while p-type semiconductors are formed by adding electron-deficient impurities.

### Step 2: Identify the Type of Impurity
In this case, we are dealing with an "electron rich impurity." This typically refers to pentavalent impurities such as phosphorus (P), arsenic (As), or antimony (Sb), which have five valence electrons.

**Hint:** Pentavalent impurities donate extra electrons to the conduction band of the semiconductor.

### Step 3: Determine the Resulting Semiconductor Type
When silicon (which has four valence electrons) is doped with a pentavalent impurity, the extra electron from the impurity becomes free to move, thus increasing the number of free electrons in the material. This results in the formation of an n-type semiconductor.

**Hint:** Recall that n-type semiconductors are characterized by an abundance of free electrons.

### Step 4: Eliminate Other Options
- **P-type Semiconductor:** Formed by doping with trivalent impurities (electron-deficient).
- **Intrinsic Semiconductor:** Refers to pure silicon without any doping.
- **Insulator:** Materials that do not conduct electricity.

Since the question specifies "electron rich impurity," the only correct answer is n-type semiconductor.

### Final Answer
Silicon doped with electron rich impurity forms **n-type semiconductor**.

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