Concept:At thermal equilibrium without an external voltage, dynamic equilibrium is established where majority carrier diffusion is perfectly counterbalanced by minority carrier drift.
Formula:$$I_{\text{net}} = I_{\text{diffusion}} - I_{\text{drift}} = 0$$
Solution:- Majority carriers diffuse across the junction due to steep concentration gradients (\( I_{\text{diffusion}} \)).
- The built-in electric field drives minority carriers across the junction in the reverse direction (\( I_{\text{drift}} \)).
- In equilibrium, \( I_{\text{diffusion}} = I_{\text{drift}} \), resulting in zero net current.
Why other options are incorrect:- Option B: A strong localized electric field exists precisely inside the depletion region.
- Option C: Thermal generation of electron-hole pairs continuously occurs at room temperature.
- Option D: A small fraction of majority carriers with high thermal kinetic energy still cross the barrier, but this equals the drift current.
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