Introduction / Context:
In semiconductor physics, electrical conduction occurs because of mobile charge carriers. Recognizing how many fundamental carrier types exist is essential for understanding diodes, transistors, and integrated circuits.
Given Data / Assumptions:
- Semiconductor materials such as silicon or germanium are considered.
- We are concerned with intrinsic or extrinsic conduction mechanisms.
Concept / Approach:
The two types of charge carriers in semiconductors are electrons in the conduction band and holes in the valence band. These are the only two entities that contribute to current in standard semiconductor theory.
Step-by-Step Solution:
Electrons move freely in the conduction band under an applied electric field.Each electron excited into the conduction band leaves behind a hole in the valence band.Holes behave as positively charged carriers.Thus, exactly two carrier types exist: electrons and holes.
Verification / Alternative check:
Intrinsic condition: n = p = ni, showing electrons and holes exist in pairs. Doped semiconductors increase one type but both still exist.
Why Other Options Are Wrong:
1: Incomplete, ignores the second carrier type.3 or 4: There are no third or fourth carrier types in classical conduction.5: Arbitrary, not relevant.
Common Pitfalls:
Confusing immobile ions with mobile carriers; ions do not conduct in crystalline semiconductors under normal bias.
Final Answer:
2
Discussion & Comments