Concept:Thermal equilibrium is a dynamic state where forward diffusion and reverse drift currents balance, resulting in zero net current through the junction.
Formula:$$J_{\text{total}} = J_{\text{diffusion}} + J_{\text{drift}} = 0$$
Solution:- Concentration gradients drive majority carrier diffusion across the junction.
- The resulting space-charge layer creates an electric field that sweeps minority carriers across in the opposite direction (drift).
- At equilibrium, the diffusion and drift currents balance: \( |I_{\text{diffusion}}| = |I_{\text{drift}}| \).
- As a result, the net current across the junction is zero.
Why other options are incorrect:- Option A: Diffusion continues at the microscopic level; it is balanced by drift rather than halted.
- Option C: The depletion layer reaches a stable equilibrium width rather than collapsing.
- Option D: A finite barrier potential (\( \approx 0.7\text{ V} \) for Si) exists at equilibrium to maintain current balance.
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