If silicon is doped with phosphorus, what type of semiconductor material will be formed?

Analysis

The question asks about the effect of adding phosphorus (a Group 15 element) to silicon (a Group 14 element) in the context of semiconductor physics.

Concept Explanation

Semiconductors like Silicon (Si) have four valence electrons. To change their electrical properties, we perform a process called doping, which involves adding small amounts of impurities.

• Intrinsic Semiconductors: Pure silicon.
• n-type Semiconductors: Formed when silicon is doped with pentavalent elements (elements with 5 valence electrons), such as Phosphorus (P), Arsenic (As), or Antimony (Sb). Because the impurity has 5 electrons, 4 bond with the silicon atoms, leaving one "extra" electron free to move and conduct electricity. Since electrons are negatively charged, it is called an n-type (negative-type) semiconductor.
• p-type Semiconductors: Formed when silicon is doped with trivalent elements (elements with 3 valence electrons), such as Boron (B) or Aluminum (Al). This creates a "hole" (a vacancy), which acts as a positive charge carrier.

Step-by-Step Solution

1. Identify the base material: Silicon is a Group 14 element with 4 valence electrons.
2. Identify the dopant: Phosphorus is a Group 15 element with 5 valence electrons.
3. Determine the effect: When Phosphorus is added to Silicon, the 5th electron of the Phosphorus atom does not participate in the covalent bonding with Silicon.
4. Conclusion: This excess electron becomes a free charge carrier. Since the material now has an abundance of negative charge carriers (electrons), it is classified as an n-type semiconductor.

Answer

The correct option is C.

Exam Tip

Remember the mnemonic: Phosphorus = Pentavalent = n-type (think "n" for negative electrons). Conversely, Boron = Trivalent = p-type (think "p" for positive holes). This will help you quickly identify the type of semiconductor in any JAMB or WASSCE question!