Carrier motion in semiconductors: When a DC voltage is applied across a semiconductor, do free electrons drift toward the positive terminal (higher potential) or toward the negative terminal?

Introduction / Context:Understanding charge carrier motion under an electric field is foundational to diodes, BJTs, and FETs. The sign of the carrier determines its drift direction relative to applied voltage.

Given Data / Assumptions:

• Uniform semiconductor with both electrons (negative) and holes (positive) as carriers.
• DC electric field established by an external voltage.
• Conventional current direction is defined from positive to negative potential.

Concept / Approach:Electrons, being negatively charged, experience a force opposite to the electric field direction and drift toward the higher electric potential (the positive terminal). Holes, treated as positive charge carriers, drift in the direction of the electric field, toward the negative terminal. This bidirectional motion contributes to the net current, which by convention is in the direction of positive charge flow.

Step-by-Step Solution:

Verification / Alternative check:In a p-n junction forward biased, electrons are injected from n to p (toward the positive terminal on p-side), while holes move from p to n (toward the negative terminal on n-side), matching the drift directions described.

Why Other Options Are Wrong:

• “Electrons toward negative terminal” (option b) reverses the physics of negative charge in an electric field.
• “Electrons stationary” (option c) ignores drift under applied fields; both carriers can move.
• “Direction cannot be defined” (option d) is incorrect; drift direction is well-defined.

Common Pitfalls:Confusing electron flow with conventional current direction; conventional current points from positive to negative, opposite to electron drift.

Final Answer:Electrons drift toward the positive terminal; holes drift toward the negative terminal.