Introduction / Context:
Carrier types and doping polarities in BJTs determine device operation, current flow, and transistor gain. For an n–p–n device, understanding which carriers dominate in each region (emitter, base, collector) is fundamental to analyzing injection, recombination, and current gains (α and β).
Given Data / Assumptions:
- An n–p–n transistor has an n-type emitter, p-type base, and n-type collector.
- “Majority carriers” refer to carriers introduced by the intentional doping of that region (not the injected minority carriers from another region).
Concept / Approach:
By definition, the base in an n–p–n BJT is p-type; therefore, holes are its majority carriers. Although the useful conduction involves electrons injected from the n-type emitter into the base (where they are minority carriers), the base remains p-type with holes as majority carriers and electrons as minority carriers within it.
Step-by-Step Solution:
Identify doping: base is p-type → majority carriers are holes.Recognize device action: emitter injects electrons into base; these electrons are minority carriers in the base and are partially collected by the collector.Therefore the correct answer is holes.
Verification / Alternative check:
Compare with a p–n–p BJT: there the base is n-type and electrons would be majority; this symmetry check confirms the reasoning.
Why Other Options Are Wrong:
Electrons: they are minority in the base of an n–p–n.Both or either: majority carriers are determined by doping, not by operating condition ambiguity.Ions: irrelevant to majority carrier conduction in a semiconductor device.
Common Pitfalls:
Confusing “majority within base” with “dominant conduction mechanism” of the overall transistor.
Final Answer:
holes
Discussion & Comments