Does the P–N junction act as a barrier to electron flow? (Majority carriers at equilibrium) Evaluate the statement: “The P–N junction is a barrier to electron flow.” Choose the best characterization, considering equilibrium and typical biasing conditions.

Introduction / Context:
The hallmark of a P–N junction is the formation of an internal potential barrier that opposes majority-carrier diffusion. This barrier explains diode rectification and underpins transistor action. Interpreting the statement correctly requires noting operating conditions (equilibrium, forward bias, reverse bias).

Given Data / Assumptions:

• Standard abrupt P–N junction.
• Equilibrium (no external bias) or reverse bias unless stated otherwise.
• Majority versus minority carriers are distinguished.

Concept / Approach:
At equilibrium, diffusion of majority carriers (electrons from n to p, holes from p to n) creates a space-charge region with an electric field that drives drift in the opposite direction. The resulting built-in potential V_bi forms a barrier impeding further majority-carrier diffusion. Under forward bias, the external source reduces this barrier, allowing significant current; under reverse bias, the barrier increases, suppressing majority-carrier flow and leaving only a small minority-carrier current until breakdown.

Step-by-Step Solution:

Verification / Alternative check:
Diode I–V shows negligible current for reverse bias before breakdown and large current for forward bias once overcoming the barrier (~0.3 V Ge, ~0.7 V Si at room temperature for typical small diodes).

Why Other Options Are Wrong:

Common Pitfalls:
Forgetting that minority carriers can still traverse the junction; conflating “barrier” with an absolute block rather than an energy threshold modified by bias.

Final Answer:
Correct