Doping basics: A pentavalent (group V) impurity introduced into a group IV semiconductor contributes how many valence electrons?
Electronics and Communication Engineering
Materials and Components
Difficulty: Easy
Choose an option
-
A5
-
B4
-
C3
-
D1
-
E2
Answer
Correct Answer: 5
Explanation
Introduction / Context:Doping modifies the electrical properties of semiconductors by adding controlled impurities. Pentavalent dopants (group V), such as phosphorus or arsenic, create n-type material by donating electrons.
Given Data / Assumptions:
- Host lattice is group IV (e.g., silicon) with four covalent bonds.
- Dopant is pentavalent (group V): five valence electrons.
- Substitutional doping: dopant replaces a silicon atom in the lattice.
Concept / Approach:The dopant's five valence electrons form four bonds with neighboring atoms, leaving one extra, loosely bound electron. This electron requires little energy to become a conduction electron, increasing carrier concentration dramatically.
Step-by-Step Solution:
Identify dopant group: V → five valence electrons.Place dopant substitutionally: four electrons complete covalent bonds.Recognize remaining electron as a donor level near the conduction band.Verification / Alternative check:
Hall-effect measurements show negative carriers dominate in n-type silicon doped with P or As.Why Other Options Are Wrong:
4 corresponds to group IV; 3 and 1 correspond to acceptors/monovalent species; 2 is not applicable here.Common Pitfalls:
Confusing donor (group V) with acceptor (group III) dopants.Final Answer:
5