Concept:At thermal equilibrium with no applied voltage, dynamic balance is established between diffusion and drift currents, resulting in zero net current.
Formula:$$I_{\text{net}} = I_{\text{diffusion}} - I_{\text{drift}} = 0$$
Solution:- A small fraction of majority carriers possess sufficient thermal energy to overcome the built-in barrier \( V_B \), creating a forward diffusion current \( I_{\text{diffusion}} \).
- Thermally generated minority carriers that reach the depletion boundary are swept across by the built-in field, creating a reverse drift current \( I_{\text{drift}} \).
- At thermal equilibrium, \( I_{\text{diffusion}} = I_{\text{drift}} \), so the net current \( I_{\text{net}} = 0 \).
Why other options are incorrect:- Option A: Abundant majority carriers exist in the neutral P and N regions outside the depletion layer.
- Option B: The dynamic resistance of bulk doped silicon is low (on the order of ohms), not infinite.
- Option D: Charge carriers recombine or are redirected; they are not destroyed out of equilibrium.
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