Concept:At thermal equilibrium, the concentration gradient drives a diffusion current across the junction, while the built-in electric field drives an equal and opposite drift current, resulting in zero net current.
Formula:$$J_{\text{net}} = J_{\text{diffusion}} + J_{\text{drift}} = 0 \implies J_{\text{diffusion}} = -J_{\text{drift}}$$
Solution:- Majority carriers diffuse across the junction due to the concentration gradient (\( I_{\text{diffusion}} \)).
- Thermally generated minority carriers are swept back across the depletion layer by the built-in electric field (\( I_{\text{drift}} \)).
- At equilibrium, these two opposing currents are equal in magnitude, so no net current flows.
Why other options are incorrect:- Option A: Charge carriers remain mobile due to thermal energy at room temperature.
- Option B: The depletion layer has a strong built-in electric field (\( \sim 10^6\text{ V/m} \)).
- Option D: Thermal generation continuously creates new electron-hole pairs throughout the crystal.
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