Concept:The built-in electric field points from the positive donor ions (N-side) to the negative acceptor ions (P-side). Forward bias applies an external electric field in the opposite direction (P-side to N-side).
Formula:$$\vec{E}_{\text{net}} = \vec{E}_{\text{built-in}} - \vec{E}_{\text{applied}}$$
Solution:- \( \vec{E}_{\text{built-in}} \) points from the N-region to the P-region.
- Forward bias applies a positive potential to the P-region and a negative potential to the N-region, establishing \( \vec{E}_{\text{applied}} \) from P to N.
- Because these vectors are in opposite directions, the net electric field decreases, narrowing the depletion layer and allowing forward current flow.
Why other options are incorrect:- Option A: Reinforcement of the internal field occurs during reverse bias, where both fields point from N to P.
- Option C: Perpendicular fields occur in Hall effect setups involving external magnetic fields, not standard axial diode biasing.
- Option D: Electric fields superpose vectorially; the applied field directly alters the space-charge potential.
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