Which one among these is an example for trivalent impurity?

Trivalent Impurities in Semiconductors

Definition: Trivalent impurities are elements from group III of the periodic table that have three valence electrons. These impurities are introduced into an intrinsic semiconductor (pure semiconductor) to create a p-type semiconductor. When a trivalent impurity is added to a semiconductor, it creates "holes" (positive charge carriers), making the semiconductor conducive to electrical current primarily through hole movement.

Working Principle: In a pure semiconductor like silicon or germanium, each atom forms covalent bonds with four neighboring atoms. When a trivalent impurity (e.g., gallium) is added, it has only three valence electrons, which are insufficient to form four covalent bonds. The absence of the fourth electron creates a "hole" in the crystal lattice. This hole acts as a positive charge carrier, and the movement of these holes constitutes electric current in a p-type semiconductor.

Examples of Trivalent Impurities:

• Gallium (Ga): A commonly used trivalent impurity for doping semiconductors to create p-type materials.
• Boron (B): Another widely used trivalent impurity for the same purpose.
• Indium (In): Occasionally used for specific semiconductor applications.

Advantages of Doping with Trivalent Impurities:

• Increases the conductivity of the semiconductor by providing positive charge carriers.
• Enables the creation of p-n junctions, which are the basis of many electronic devices like diodes and transistors.
• Facilitates the customization of semiconductor properties for specific applications.

Correct Option Analysis:

The correct option is:

Option 3: Gallium

Gallium is a trivalent impurity, meaning it has three valence electrons. When introduced into a semiconductor, it creates holes by leaving a bond incomplete, which facilitates the formation of a p-type semiconductor. This is a classic example of a trivalent impurity used for doping semiconductors.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: Phosphorus

Phosphorus is a pentavalent impurity, meaning it has five valence electrons. When added to a semiconductor, it donates an extra electron, creating an n-type semiconductor. This makes phosphorus unsuitable as a trivalent impurity.

Option 2: Antimony

Antimony is also a pentavalent impurity. Like phosphorus, it donates an extra electron when introduced into a semiconductor, leading to the formation of an n-type semiconductor. Therefore, it cannot be classified as a trivalent impurity.

Option 4: Arsenic

Arsenic is another pentavalent impurity. It behaves similarly to phosphorus and antimony by contributing an extra electron to the semiconductor lattice, creating an n-type semiconductor. It is not a trivalent impurity.

Option 5: None

This option is incorrect because Gallium (Option 3) is indeed a valid example of a trivalent impurity, as explained above.

Conclusion:

Among the options provided, Gallium is the correct example of a trivalent impurity. Trivalent impurities like Gallium play a crucial role in the semiconductor industry by enabling the creation of p-type semiconductors. Understanding the behavior of trivalent and pentavalent impurities is essential for designing and optimizing electronic devices such as diodes, transistors, and integrated circuits.