Silicon is a semiconductor. If a small amount of As is added to it, then its electrical conductivity

Options

A. Decreases
B. Increases
C. Remains unchanged
D. Becomes zero

Answer

To solve the question regarding the effect of adding arsenic (As) to silicon (Si) on its electrical conductivity, we can follow these steps:

### Step 1: Understand the Nature of Silicon
Silicon is a semiconductor material that has four valence electrons. In its pure form, silicon has a limited ability to conduct electricity because it lacks free charge carriers (electrons).

**Hint:** Remember that semiconductors have a specific number of valence electrons that determine their conductivity.

### Step 2: Identify the Role of Arsenic
Arsenic is a group 15 element that has five valence electrons. When a small amount of arsenic is added to silicon, it donates one extra electron to the conduction band.

**Hint:** Group 15 elements can donate extra electrons when introduced into group 14 semiconductors like silicon.

### Step 3: Analyze the Effect on Conductivity
The introduction of arsenic into silicon creates additional free charge carriers (electrons) in the material. This process is known as "n-type doping," where the conductivity of the semiconductor increases due to the presence of these extra electrons.

**Hint:** Doping a semiconductor with elements that have more valence electrons than the semiconductor can enhance its conductivity.

### Step 4: Conclusion
Since the addition of arsenic increases the number of free electrons in silicon, the electrical conductivity of silicon will increase.

**Final Answer:** The electrical conductivity of silicon will **increase** when a small amount of arsenic is added.

### Summary of Steps
1. Silicon is a semiconductor with four valence electrons.
2. Arsenic, having five valence electrons, donates an extra electron when added to silicon.
3. This results in an increase in free charge carriers (electrons), leading to increased conductivity.
4. Therefore, the correct answer is that the electrical conductivity **increases**.