Concept:Carrier diffusion occurs when a concentration gradient exists between adjacent semiconductor regions, causing charge carriers to move from areas of high concentration to areas of low concentration.
Formula:$$J_{n,\text{diff}} = e D_n \frac{dn}{dx}, \quad J_{p,\text{diff}} = -e D_p \frac{dp}{dx}$$
Solution:- The N-region has a high concentration of free electrons, while the P-region has a low concentration of free electrons.
- The P-region has a high concentration of holes, while the N-region has a low concentration of holes.
- This concentration gradient drives the diffusion of electrons into the P-region and holes into the N-region until space-charge equilibrium is established.
Why other options are incorrect:- Option A: Diffusion occurs spontaneously during junction formation without an external power supply.
- Option C: Thermal energy (\( k_B T \)), rather than electromagnetic radiation, provides the energy for carrier motion.
- Option D: Carrier motion is governed by electrostatics and concentration gradients, with gravitational effects being negligible.
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