In a p-type semiconductor, the?

Analyze the question: It asks what is true of a p-type semiconductor, which is a basic fact about doping.

Concept:

• A pure (intrinsic) semiconductor such as silicon or germanium has equal numbers of electrons and holes.
• Doping with a trivalent impurity (e.g., boron, aluminium, gallium, indium) gives a p-type semiconductor. Each trivalent atom has only 3 valence electrons, so it leaves a vacancy in a covalent bond. This vacancy is called a hole.
• Doping with a pentavalent impurity (e.g., phosphorus, arsenic, antimony) gives an n-type semiconductor, where electrons are the majority carriers.

Step by step:

1. A trivalent atom replaces a silicon atom in the crystal lattice.
2. It forms only 3 complete covalent bonds, so one bond is missing an electron, which creates a hole.
3. Many holes are therefore available to carry current (they are "positive" charge carriers).
4. So in p-type material, holes are the majority carriers and electrons are the minority carriers.

Checking the options:

• A. Holes equal to electrons: this is true of intrinsic semiconductors, not p-type. ✗
• B. Resistivity increases: doping adds charge carriers, so resistivity decreases. ✗
• C. Electrons are the majority carriers: this describes n-type. ✗
• D. Holes are the majority carriers: ✓

Tip: Think "P = Positive holes" and "N = Negative electrons". Also remember that trivalent impurities give p-type (3 → p) and pentavalent impurities give n-type.