Concept:The large concentration gradient across the newly formed junction causes free electrons from the N-region to diffuse into the P-region and holes from the P-region to diffuse into the N-region.
Formula:$$J_{\text{diffusion}} = q D_n \frac{dn}{dx} + q D_p \frac{dp}{dx}$$
Solution:- As free electrons and holes diffuse across the junction, they recombine near the interface.
- This recombination uncovers uncompensated, immobile positive donor ions on the N-side and immobile negative acceptor ions on the P-side.
- This region, devoid of mobile charge carriers, is called the depletion layer.
Why other options are incorrect:- Option B: Drift occurs after the internal electric field is established or when an external voltage is applied.
- Option C: Thermal ionization occurs uniformly throughout the bulk semiconductor, not specifically at the junction.
- Option D: Nuclear fusion does not occur in solid-state chemical/semiconductor physics.
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